%M..-^

UC-NRLF

MEMCAL SCHOOL

IN MEMORIiUyi
DR. S.J.S. ROGERS

/

IBbik,.

Digitized by the Internet Archive

in 2007 with funding from

IVIicrosoft Corporation

http://www.archive.org/details/elemephysioOOcarprich

ELEMENTS OF PHYSIOLOGY.

By the same Author,
PRINCIPLES

OF

GENERAL AND COMPARATIVE PHYSIOLOGY

WITH NUMEROUS ILLUSTRATIONS. (AT PRESS.)

PRINCIPLES OF HUMAN PHYSIOLOGY.

WITH NUMEROUS ILLUSTRATIONS.

A POPULAR TREATISE ON VEGETABLE PHYSIOLOGY.

WITH NUMEROUS CUTS.

PUBLISHED BY LEA AND BLANCHARD.

ELEMENTS

OF

PHYSIOLOGY,

INCLUDING

PHYSIOLOGICAL ANATOMY,

FOR THE USE OF THE MEDICAL STUDENT.

BY

WILLIAM B./CARPENTER, M.D.,F.R.S.,

rULLERIAN PROFESSOR OF PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN j

MEMBER OF THE AMERICAN PHILOSOPHICAL SOCIETY, AND

CORRESPONDING MEMBER OF THE NATIONAL INSTITUTE OF THE UNITED STATES;

ETC. ETC.

WITH ONE HUNDBED AND EIGHTY ILLUSTBATIONS.

PHILADELPHIA:

LEA AND BLANCHARD.

1846.

PHILADELPHIA :

T. K. AND P. G. COLLINS,

PRINTERS.

AMERICAN PUBLISHERS' ADVERTISEMENT.

The sheets of this volume, in their passage through the press,
have been carefully examined by Dr. Meredith Clymer, the Editor
of Dr. Carpenter's "Principles of Human Physiology." The perfect
adaptation of the work to its purposes as an elementary text-book,
and the manner in which it is brought up to the day, have rendered
unnecessary any notes or additions ; the efforts of the publishers,
therefore, have been directed to a correct reprint of the London
edition.

That it may correspond in size with the Author's other works on
Physiology, the publishers have employed a type larger than that
used in the London edition, and consequently they have been induced
to substitute the word '^Elements^^ in place of ^^ Manual, ^^ which was
adopted by the Author more with reference to its original size than
to its contents, as stated in his Preface.

Philadelphia, •

April, 1846.

il ()•>{}

PEEFACE.

The present volume owes its origin to a desire, on the part of the
Publisher, that an elementary treatise on Physiology should be added
to the series of admirable Students' Manuals, on the various depart-
ments of Medical Science, which he has already issued. But for
this desire, the Author would have preferred not again to present
himself so soon before the public, in a capacity in which he fears
that he has already trespassed too much on their indulgence ; his
wish being rather to devote as much time as possible to original
inquiry in various departments of Physiology, which stand in great
need of elucidation.

Although this Manual combines, in some degree, the scope of the
Author's two larger works on the same subject, yet it cannot be
regarded as a mere abridgment of them ; having been written with
very little reference to them, and on a plan which is in many respects
different. His object has been to convey to the Student as clear an
idea as possible of the principles of the science, to point out the
manner in which these principles should be applied, and to give an
outline of the most important facts which indicate the nature of the
various changes taking place in the living organism. In following out
this intention he has thought it right to adopt a plan which, so far as he
knows, is a novel one : — namely, to commence his exposition of the
characters of Organized Structures and of Vital Phenomena by a full
account of the Development and Metamorphoses of Cells, and of the
purposes which these effect in the living body, either in their original
or in their altered condition. He is of opinion that the inferences,
"which may be drawn from the observations on this subject, that have
rapidly accumulated during the last few years, are entitled to hold
the same rank in Physiological Science as that taken by the doctrine
of Mutual Attraction in General Physics, or of Elective Affinity in
Chemistry ; and that the enunciation and development of these should

viii PREFACE.

consequently hold the first place in an Elementary Treatise on Physi-
ology. The third chapter, constituting more than one-fourth of the
entire Treatise, is therefore devoted to this subject. The topics em-
braced in the first two chapters, and in the whole of the Second
Book, are treated of on a much more extended scale in the Author's
"Principles of General and Comparative Physiology," and *' Prin-
ciples of Human Physiology," to which he would refer those who
desire further information upon them. As the matter of which those
volumes are composed is itself condensed to the utmost possible de-
gree, it is manifestly impossible that the present Manual should con-
tain more than a mere outline of the subjects of which they treat.
The Author has endeavoured to select what is of the most import-
ance to the Student, and lies most readily within his comprehension ;
and has rather desired to impress the minds of his readers with a
clear notion of what he considers the leading or typical facts of the
science, than to load his memory with details.

The Author may be permitted to direct attention to the copiousness
and beauty of the illustrations, which the liberality of the Publisher
has allowed him to introduce. The greater part of the wood-engrav-
ings have been executed, expressly for this volume, by Mr. Vasey,
whose skill and fidelity have recently shown themselves to be as
great in the treatment of anatomical subjects as they have been long
known to be in the representation of objects of natural history.

Stoke Newington,
Feb. 20th, 1846.

TABLE OF CONTENTS

BOOK I.

GENERAL PHYSIOLOGY.

Chapter Page

I. Ox THE Nature and Objects of the Science of Phtsiologt - - 17

1. Of Organic Structures - - - - - - 18

2. Of Vital Actions ------- 25

3. Connection between Vitality and Organization - - - 48

II. Of the Vital Stimuli -------58

1. Of Light, as a Condition of Vital Action - - - 61

2. Of Heat, as a Condition of Vital Action - - - - 72

3. Of Electricity, as a Condition of Vital Action - - - 98

4. Of Moisture, as a Condition of Vital Action - - - loi

III. Of the Elementary Parts of Animal Structures - - - 109

1. Of the original Components of the Animal Fabric - - IH

2. Of the Simple Fibrous Tissues - - - - - 123

3. Of the Basement or Primary Membrane - - - - 133

4. Of Simple Isolated Cells, employed in the Organic Functions - 136
6. Of Cells connected together, as permanent constituents of the

Tissues - -- - - - - - 159

6. Of Cells coalesced into Tubes, with Secondary Deposit - - 203

BOOK II.

SPECIAL PHYSIOLOGY.

IV. Of Food, and the Digestive Process ----- 243

1. Sources of the Demand for Aliment - - - - 243

2. Of the Digestive Apparatus, and its Actions in general - - 261

3. Of the Movements of the Alimentary Canal - - - 266

4. Of the Secretions poured into the Alimentary Canal, and of the

Changes which they effect in its contents - . . 273

5. Of Hunger, Satiety, and Thirst - - - - - 282

V. Of Absorption and Sanguification ----- 285

1. Of Absorption from the Digestive Cavity - . . 285

2. Of the Passage of Chyle along the Lacteals, and its admixture

with the Lymph collected from the General System - - 289

3. Of the Spleen, and other Glandular appendages to the Lymphatic

System ...----- 294

4. Of the Composition and Properties of the Chyle and Lymph - 299

5. Of Absorption from the External and Pulmonary Surfaces - 303

6. Of the Composition and Properties of the Blood - - - 304

Page

• •

•

312

t Fluid

.

312

.

.

314

.

.

329

.

.

337

.

m

340

-

-

349

.

.

353

.

.

353

.

.

355

.

.

361

.

.

362

X TABLE OF CONTENTS.

Chaptek
VI. Of the CiHCULATio^r of the Blood

1. Nature and Objects of the Circulation of Nutrient Fluid

2. Different forms of the Circulating Apparatus

3. Action of the Heart

4. Movement of the Blood in the Arteries

5. Movement of the Blood in the Capillaries

6. Movement of Blood in the Veins -

VII. Of Nutritiok --.-_.

1. Selecting Power of Individual Parts

2. Varying Activity of tne Nutritive Processes

3. Of Death, or Cessation of Nutrition

4. Disordered Conditions of the Nutritive Processes

Vni. Of Respiration - - - - - - - - 367

1. Essential Nature and Conditions of the Respiratory Process - 367

2. Different forms of the Respiratory Apparatus in the lower Animals 373

3. Mechanism of Respiration in Mammalia and in Man - - 385

4. Chemical Phenomena of Respiration - - - - 392

5. Effects of Insufficiency, or Suspension, of the Aerating Process - 399

IX. Of Secretiox ---.---. 403

1. Of the Secreting Process in general; and of the Instruments by

which it is effected -..-.- 403

2. Of the Liver, and the Biliary Excretion - - . - 410

3. Of the Kidneys, and the Urinary Excretion - - - 416

4. Of the Cutaneous and Intestinal Glandulae - - - 425

5. General Summary of the Excreting Processes - - - 430

X. Of the DETELOPMEiirT OF Light, Heat, and Electricitt in the Animal

BoDr ........ 434

^I. Of Reproduction -.-.--- 443

1. General View of the Nature of the Process ... 443

2. Action of the Male ..----- 446

3. Action of the Female ..---. 449

XII. Of the Nervous System -._.-- 476

1. General view of the operations, of which the Nervous System is

the Instrument --.--.- 476

2. Comparative Structure and Actions of the Nervous System - 481

3. Functions of the Spinal Cord and its Nerves ... 498

4. Functions of the Medulla Oblongata .... 507

5. Functions of the Sensory Ganglia .... 510

6. Functions of the Cerebellum ----- 518

7. Functions of the Cerebrum . . - - - 520

8. Functions of the Sympathetic System - - - - 526

XIII. Of Sensation, General and Special ----- 528

1. Of Sensation in general ------ 528

2. Of the Sense of Touch ------ 533

3. Of the Sense of Taste .-.--- 535

4. Of the Sense of Smell ..---- 537

5. Of the Sense of Hearing - 539

6. Of the Sense of Sight ------ 542

XIV. Of the Voice, and Speech ------ 552

LIST OF WOOD ENGRAVINGS.

Fig. Page

1. Simple isolated Cells, containing reproductive molecules - - 33

2. Fibrous structure of exudation-membrane . . - > 120

3. Fibrous membrane lining egg-shell (original) - - - - 120

4. White fibrous tissue of areolar tissue and tendon - - . 124

5. White fibrous tissue of ligament _ _ - _ _ 125

6. Yellow fibrous tissue of ligamentum nuchae - - - - 125

7. Capillary vessels of Skin; after Berres - - - - - 132

8. Capillary vessels of Intestinal villi; after Berres ... 132

9. Capillary vessels around orifices of Mucous follicles; after Berres - 132

10. Capillary vessels around follicles of Parotid Gland; after Berres - 132

11. Distribution of Sensory nerves in Skin; after Gerber - - ' - 133

12. Primary membrane, with germinal spots ; after Goodsir - - 134

13. Primary membrane, showing component cells ; after Goodsir - - 135

14. Simple isolated cells, containing reproductive molecules - - 137

15. Cells from fluid of Herpes; after Addison ... - 133

16. Oblique section of Epidermis; after Henle - - - - 145

17. Epidermic cells from Conjunctiva; after Gerber - - - 145

18. Portion of Choroid-coat, showing pigment cells; after Gerber - - 147

19. Separate Pigment-cells ------- 147

20. Detached epithelium-cells from mucous membrane of mouth - - 149

21. Pavement-epithelium from bronchial tubes; after Lebert - - 149

22. Layer of cylindrical epithelium, with cilia; after Henle - - 150

23. Follicles from liver of Crab, with contained secreting cells; after Goodsir 153

24. Follicles of Mammary gland, with contained secreting cells ; after Lebert 153

25. Secreting Cells of Human Liver ------ 154

26. Formation of Spermatozoa within cells; after Wagner - - 154

27. Diagram of Intestinal Mucous membrane, during digestion and absorption

of chyle; after Goodsir ------ 156

28. Diagram of Intestinal Mucous membrane, in intervals of digestion; after

Goodsir -------- 156

29. Extremity of Placental villus ; after Goodsir - - - - 157

30. Parent-cells, with contained secondary cells, of cancerous structure ; after

Lebert --------- 160

31. Progressive stages of cell-growth, in shell-membrane (original) - 162

32. Progressive stages of coalescence of cells, in shell-membrane (original) 162

33. Transition from cellular to fusiform tissue; after Lebert - - 164

34. Fusiform tissue of plastic exudations ; after Lebert - - - 164

35. Areolar and Adipose tissue; after Berres - - - . 164

36. Capillary network around Fat-cells; after Berres - - - 165

37. Section of Cartilage; after Schwann ----- 168

38. Distribution of vessels on surface of Cartilage; after Toynbee - - 170

39. Nutrient vessels of Cornea; after Toynbee - - - - 171

40. Cancellated structure at extremity of Femur - - - - 173

41. Lacunae of Osseous substance ------ 174

42. Section of Bony Scale of Lepidosteus (original) - - - 174

43. Network of Haversian canals, from vertical section of Tibia - - 176

44. Transverse section of long bone - - - - - 177

Xll

LIST OF WOOD ENGRAVINGS.

Fig.
45.
46.
47.
48.
49.
60.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.

72.

73.

74.

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

85.

86.

87.

88.

89.

90.

91.

92.

93.

94.

95.

96.

97.

98.

99.
100.
101.
102.
103.
104.
105.

. Shell of Echinus (original) - - - .

, Sections of Shell of Pinna (original)
Tubular shell-structure from Anomia (original)
Section of Cartilage, near seat of Ossification -
Section of Cartilage, at the seat of Ossification -
Vessels of Dental Papilla; after Berres
Oblique section of Dentine; after Owen
Vertical section of Human Molar Tooth; after Nasmyth
Development of Teeth ; after Goodsir
Fasciculus of Striated Muscular fibre ; after Mandll
Non-striated Muscular fibres; after Bowman
Ultimate fibriilae of striated fibre (original)
Muscular fibre cleaving into disks; after Bowman
Transverse section of muscular fibres; after Bowman
Structure of ultimate fibriilae of striated fibre (original)
Nucleated fibres from non-striated muscle ; after Bowman
Nuclei in striated muscular fibres of foetus; after Bowman
Capillaries of Muscle ; after Berres
Distribution of nerves in Muscle; after Burdach
Capillaries of Nervous centres ; after Berres
Components of gray substance of Brain; after Purkinje
Structure of Ganglion of Sympathetic; after Valentin -
Distribution of Sensory Nerves in lip; after Gerber
Capillaries at margin of lips; after Berres
Diagram of Nervous System (original) - - -

Section of Human Stomach . . - .

Mucous coat of small intestine, showing Villi, and orifices of follicles ;
after Boehm ......

Stomach of Sheep - - . . .

Section of Stomach of Sheep, showing demi-canal ; after Flourens

Lobule of Parotid Gland - - . . -

Gastric glandulae; after Wagner . - .

Orifices of gastric tubuli; after Boyd -

Distribution of Capillaries in Intestinal Villi; after Berres

Commencement of lacteal, in intestinal villus; after Krause

Diagram of Lymphatic gland; after Goodsir

Epithelial cells of intra-glandular lymphatic; after Goodsir

Course of Thoracic duct . _ . -

Appearance of inflamed Blood; after Addison -

Vascular area of Fowl's egg; after Wagner

Diagram of the Circulation in Fish . - -

Diagram of the Circulation in Reptile . - -

Diagram of complete Double Circulation

Anatomy of Human Heart and Lungs - . -

Capillaries of Muscle ; after Berres - - -

Capillaries of Nervous centres; after Berres

Capillaries of Glandular follicles; after Berres

Capillaries of Conjunctival membrane ; after Berres

Capillaries of Choroid coat; after Berres

Capillaries around orifices of mucous follicles; after Berres

Capillaries in Skin of finger; after Berres

Capillaries in fungiform papilla of Tongue ; after Berres

Doris, showing branchial tufts; after Alder and Hancock

One of the arborescent processes of gills of Doris; ditto

Respiratory apparatus of Insects

Diagram of different forms of Respiratory Apparatus (original)

Capillaries of Gill of Eel (original) _ - -

Section of Lung of Turtle; after Boganus - r

Capillaries of Human Lung (original) - - -

Simple glandular follicles; after Miiller

Embryonic development of Liver; after Miiller

Rudimentary Pancreas, from Cod; after Miiller

Pass
181
183
184
187
187
192
193
196
198
204
204
205
205
205
206
207
208
208
209
226
226
227
228
228
236
263

264
269
270
273
275
275
287
288
289
289
290
311
319

327
328
341
342
342
342
342
342
342
343
372
375
377
378
379
382
386
407
407
407

LIST OF WOOD ENGRAVINGS. xiii

Fio. Page

106. Mammary Gland of Ornethorhyncees ; after Miiller - - - 407

107. Meibomian Glands; after Miiller - - . . . 408

108. Portion of Co wper's Gland; after Miiller - - - . 4O8

109. Lobule of Lachrymal Gland; after Miiller - - ' - - 408

110. Hepatic Follicles from Crab; after Goodsir - - - - 409

111. Ultimate Follicles from Mammary gland; after Lebert - - 409

112. Surface of Lobule of Liver of Squilla; after Miiller - - - 410

113. Interior of Lobule of Liver of Squilla; after Miiller - - - 410

114. Liver of Tadpole; after Miiller - - - - - 411

115. Distribution of Blood-vessels in Lobules of Liver; after Kiernan - 412

116. Connections of Lobules of Liver with Hepatic vein; after Kiernan - 412

117. Distribution of Hepatic ducts around Lobules of Liver; after Kiernan 413

118. Secreting Cells of Liver ...... 413

119. Development of Kidney, in embryo of Lizard; after Miiller - - 416

120. Kidney of foetal Boa; after Muller ..... 417

121. Portion of Kidney of Coluber; after Miiller ... - 417

122. Fasciculus of tubuli uriniferi of Bird; after Muller . . - 417

123. Section of Kidney ....... 4I8

124. Section of portions of Kidney, slightly magnified; after Wagner - 418

125. Distribution of vessels in Kidney ; after Bowman ... 418

126. Vertical section of Skin - - - - - - - 425

127. Hepatic Cells gorged with Fat; after Bowman - - - - 432

128. Simple isolated cells, with reproductive molecules - - - 443

129. Formation of Spermatozoa within seminal cells; after Wagner - 446

130. Anatomy of the Testis ....... 447

131. Plan of early Uterine Ovum ; after Wagner .... 457

132. Vascular Area of Fowl's Egg ; after Wagner .... 460

133. Diagram of Ovum, at commencement of separation of digestive cavity;

after Wagner ........ 462

134. Diagram of Ovum, showing the formation of the Amnion ; after Wagner 462

135. Diagram of Human Ovum, in second month, showing the Allantois; after

Wagner ........ 463

136. Extremity of Placental Villus; after Goodsir .... 464

137. External membrane and cells of placental villus ; after Goodsir . 464

138. Diagram illustrating the arrangement of the placental decidua ; after

Goodsir ..-...-. 465

139. Plan of the FoBtal Circulation ...... 466

140. Termination of portion of milk-duct in follicles ; after Sir A. Cooper - 470

141. Portion of the Ganglionic tract of Polydesmus; after Newport - - 488

142. Human embryo at sixth week ; after Wagner - - - - 496

143. Diagram of the origin and termination of Spinal and Cerebral nerve - 502

144. Section of the base of the Brain ..... 512

145. Mesial surface of longitudinal section of Brain .... 522

146. Capillary network at margin of Lips; after Berres ... 533

147. Distribution of tactile nerves in Skin ; after Gerber ... 534

148. Capillaries of fungiform papilla of Tongue; after Berres . - - 536

149. Distribution of Olfactory nerve ...... 637

150. Refraction of rays of light through convex lens .... ,543

151. Formation of images in eye ...... 544

152. Capillary network of Retina; after Berres - - - - 546

153. Structure of the Larynx; after Willis ..... 553

Two plates embracing 27 figures, making altogether 180 figures.

EXPLANATION OF PLATE L

The Figures in this Plate represent the Cells floating in the various animal fluids ;
and they are all, with the exception of Figs. 4 and 5, copied from the representations
given by M. Donne in his Atlas de I'Anatomie Microscopique. These representations
are transcripts of Daguerreotype pictures, obtained from the objects, by a solar micro-
scope, with a magnifying power of 400 diameters.

Fig. 1. Red Corpuscles of Human Blood, viewed by their flattened surfaces (§ 215).

Fig. 2. Red Corpuscles of Human Blood, adherent by their flattened surfaces, so as
to form rolls ; — at a, the entire surfaces are adherent; at 6, their surfaces
adhere only in part.

Fig. 3. Red Corpuscles of Human Blood, exhibiting the granulated appearance which
they frequently present, a short time after being withdrawn from the vessels.

Fig. 4. Colourless Corpuscles of Human Blood (§ 212).

Fig. 5. The same, enlarged by the imbibition of water.

Fig. 6. Red Corpuscles of Frog's Blood (§ 215).

Fig. 7. The same, treated with dilute acetic acid ; the first effect of which is to render
the nucleus more distinct, as at b ; after which the outer vesicle becomes
more transparent, and its solution commences, as at a.

Fig. 8. The same, treated with water ; at a is seen a corpuscle nearly unaltered, ex-
cept in having the nucleus more sharply defined ; at b, others which have
become more spherical, under the more prolonged action of water; ate,
the nucleus is quitting the centre, and approaching the circumference of
the disk ; at c? it is almost freeing itself from the envelop ; and at e it has
completely escaped.

Fig. 9. Globules of Mucus, newly secreted (§ 237).

Fig. 10. The same, acted on by acetic acid.

Fig. 11. Globules of Pus, from a phlegmonous abscess (§ 632).

Fig. 12. The same, acted on by acetic acid.

«^"/cf *V7?'-'<'''7=^/

:mw^'

Zl

m

J

^

01

\

* \TDiFy

^'

0^ ^^

<^

i^@

n^^

^j^ (»

7" y^rrj

EXPLANATION OF PLATE IL

The Figures in this Plate represent the principal forms of the Nervous Centres in
different classes of animals. The 1st is copied from a recent Memoir by M. Blanch-
ard; the 2d, 3d, and 4th, from Mr. Newport's delineations; the 5th to the 13th from
the interesting work of M. Guillot on the Comparative Anatomy of the Encephalon
in the different classes of Vertebrata; and the two last from the work of M. Leuret
on the same subject.

Fig. 1. Nervous System of Solen; a, a, cephalic ganglia, connected together by a
transverse band passing over the (Esophagus, and connected with the other
ganglia by cords of communication ; b, pedal ganglion, the branches of
which are distributed to the powerful muscular foot; c, branchial ganglion,
the branches of which proceed to the gills d, d, the siphons c, e, and other
parts. On some of these branches, minute ganglia are seen ; as also at
/,/, on the trunks that pass forwards from the cephalic ganglia (§ 852).

Fig. 2. Nervous System of the Larva of Sphinx ligustri,- a, cephalic ganglia; 1 — 12,
ganglia of the ventral cord (§ 856).

Fig. 3. Thoracic portion of the Nervous System of the Pupa of Sphinx ligustri; a,
b, c, three ganglia of the ventral cord ; d, d, their connecting trunks; e, e,
respiratory ganglia (§ 862).

Fig. 4. Anterior portion of the Nervous System of the Imago of Sphinx ligustri; a,
cephalic ganglia ; b, b, eyes ; c, anterior median ganglion, and d, d, poste-
rior lateral ganglia of stomato-gastric system; e,f, large ganglionic masses
in the thorax, giving origin to the nerves of the legs and wings (§ 863).

Fig. 5. Brain of the Perchy seen from above (§ 869.)

Fig. 6. The same, as seen from below.

Fig. 7. Interior of the same, as displayed by a vertical section.

The following references are common to the three preceding, and to the succeed-
ing figures.

a, a. Olfactory lobes or ganglia.

b, by Cerebral ganglia or Hemispheres.

c, c. Optic lobes.

d, Cerebellum.

e, Spinal Cord.
/, Pineal gland.

f, Lobi inferiores (their precise character not determined).
, Pituitary body.
i, Optic Nerves.
Fig. 8. Brain of the Common Lizard, seen from above (§ 871).
Fig. 9. The same, as seen from below.
Fig. 10. The same, as displayed by a vertical section.
Fig. 11. Brain of the Common Goose, seen from above (§ 872).
Fig. 12. The same, as seen from below.
Fig. 13. The same, as displayed by a vertical section.
Fig. 14. Brain of the Sheep, viewed sideways (§ 873).
Fig. 15. The same, as displayed by a vertical section.

In addition to the parts indicated by the preceding references, we have here to
notice;— A;, the corpus callosum; /, the septum lucidum, and m, the Pons Varolii.

fj^atjE ir.

a--^

li

15

■^'i/tdaj-ri- lUk.Pfiim

BOOK I.

GENERAL PHYSIOLOGY,

CHAPTER I.

' ON THE NATURE AND OBJECTS OF THE SCIENCE OF PHYSIOLOGY.

1. The general distribution of the objects presented to us by ex-
ternal Nature, into three kingdoms, — the animal, the vegetable, and
the mineral, — is familiar to every one ; and not less familiar is the
general distinction between living bodies, and dead inert matter.
True it is, that we cannot always clearly assign the limits, which sepa-
rate these distinct classes of objects. Even the professed naturalist
is constantly subject to perplexity, as to the exact boundary between
the animal and the vegetable kingdoms; and the distinction between
animal and vegetable structures, on the one hand, and mineral masses
on the other, — or between living bodies, and aggregations of inert mat-
ter,— is by no means so obvious in every case, as to be at once per-
ceptible to the unscientific observer. Thus, a mass of Coral, if its
growing portion be kept out of view^, or a solid Nullipore attached to
the surface of a rock, might be easily confounded with the mineral
bodies to which they bear so close a resemblance; and a minute ex-
amination might be required to detect the difference. Nevertheless,
a well-marked distinction does exist between the organized structures
of plants and animals, and the inorganic aggregations of Mineral
matter ; as well as between the condition of a living being, whether
Animal or Plant, and that of dead or inert Mineral bodies. It is upon
these distinctions, which are usually obvious enough, that the sciences
of Anatomy and Physiology are founded ; these sciences taking
cognizance, — the former of those structures which are termed organ-
ized^— and the latter of the actions which are peculiar to those struc-
tures, and which are distinguished by the term vital. It will be
desirable to consider, in a somewhat systematic order, the principal
ideas which we attach to these terras ; as we shall be thus led most
directly to the distinct comprehension of the nature and object of
Physiological science.
2

18 NATURE AND OBJECTS OF THE

1. Of Organic Structures.

2. Organized structures are characterized, in the first place, by the
peculiarities of their form. Wherever a definite form is exhibited by
Mineral substances, it is bounded by straight lines and angles, and is
the effect of the process termed crystalization. This process results
from the tendency which evidently exists in particles of matter, espe-
cially when passing gradually from the fluid to the solid state, to
arrange themselves in a regular and conformable manner in regard to
one another. There is, perhaps, no inorganic element or combination,
which is not capable of assuming such a form, if placed in circum-
stances adapted to the manifestation of this tendency among its parti-
cles; but if these circumstances should be wanting, and the simple
cohesive attraction is exercised in bringing them together, without
any general control over their direction, an indefinite or shapeless figure
is the result. Neither of these conditions finds a parallel in the
Organized creation. From the highest to the lowest we find the
shape presenting a determinate character for each species or race^
with a certain limited amount of variation amongst individuals ; and
this shape is such, that, instead of being circumscribed within plane
surfaces, straight lines, and angles, organized bodies are bounded by
convex surfaces, and present rounded outlines. We may usually
gather, moreover, from their external form, that they are composed
of a number of dissimilar parts, or organs ; which are combined to-
gether in the one individual body, and are characteristic of it. Thus,
in the Vertebrated or Articulated animal we at once distinguish the
head and extremities from the trunk, which constitutes the principal
mass ; and where there exist no external organs of such distinctness,
as in some Mollusks, the rounded character of the general form is
sufficiently characteristic. The very simplest grades of animal and
vegetable life present themselves under a form, which approaches
more or less closely to the globular. It is among the lower tribes of
both kingdoms, that we find the greatest tendency to irregular de-
partures from the typical form of the species ; and thus is presented
an approach, on the one hand, to that indefiniteness which is charac-
teristic of uncrystaline mineral masses ; and, on the other, to that
variety of crystaline forms which the same mineral body may pre-
sent, according to the circumstances which influence its crystaliza-
tion.

3. With regard to size, again, nearly the same remarks apply. The
magnitude of Inorganic masses is entirely indeterminate, being alto-
gether dependent upon the number of particles which can be brought
together to constitute them. On the other hand, the size of Organized
structures is restrained, like their form, within tolerably definite limits,
which may nevertheless vary to a certain extent among the indi-
viduals of the same species. These limits are least obvious in
vegetables, and in the lower classes of animals. A forest tree may

SCIENCE OF PHYSIOLOGY. 'f9

go on extending itself to an almost indefinite extent ; certain species
of sea-weed attain a length of many hundred feet, and their growth
does not appear to undergo any check; and the same may he said of
those enormous masses of coral, which compose so many islands and
reefs in the Polynesian Archipelago, or of which the debris seem to
have constituted many of the calcareous rocks of ancient formation.
But in these cases the increase is produced, not so much by the con-
tinued development of the individual, as by the continued production
of new individuals, which remain in connection with the original.
Thus each bud of a tree may be regarded as a distinct individual ;
because, if placed under favourable circumstances, it can maintain
its life by itself, and can perform all the actions proper to the species;
and, consequently, the indefinite extension of the tree by the multi-
plication of buds is not in reality that exception to the rule just laid
down, which it would appear to be. Precisely the same may be said
in regard to the extension of a coral mass ; for this is accomplished
by the multiplication of polypes, by a process of budding from the
original ; and yet these remain connected with other, so as to form a
compound whole, bearing a strong analogy to a tree. The same
cannot be said, however, of the extension of a sea- weed, for this can-
not be regarded as composed of a collection of distinct individuals;
and we may therefore consider it as an illustration of the tendency
to indefiniteness in point of size^ which has been already pointed out
in regard to fornix as characteristic of the lower grades of organized
structure, and as therefore leading us towards the inorganic world.
Where this is the case, we find that the increase depends, as in
Minerals, upon the multiplication of similar parts. Thus, in the sea-
weed, each portion of the frond is almost a precise repetition of
ev^ery other; and there is scarcely any of that mutual dependence
among the diflferent parts, which makes up our idea of one individual.
4. It is, however, in the internal arrangement or aggregation of the
particles, respectively composing Organized structures and Inorganic
masses, that we find the diflference between the two most strongly
marked. Every particle of a Mineral body (in which there has not
been a mixture of ingredients) exhibits the same properties as those
possessed by the whole ; so that the chemist, in experimenting with
any substance, cares not, except as a matter of convenience merely,
whether a grain or a ton be the subject of his researches. The mi-
nutest atom of carbonate of lime, for instance, has all the properties
of a crystal of this substance, were it as large as a mountain. Hence
we are to regard a mineral body as made up of an indefinite number
of constituent particles, similar to it and to each other in properties,
and having no further relation among themselves than that w^hich they
derive from their juxtaposition. Eachparticle, then, maybe considered
as possessing a separate individuality ; as w^e can predicate of its
properties all that can be said of the largest mass. The organized
structure, on the other hand, receives its designation from being made
up of a number of distinct parts or organs, each of which has a tex-

20 NATURE AND OBJECTS OF THE

ture or consistence peculiar to itself; and it derives its character from
the whole of these collectively. Every one of these, as we shall
hereafter see, is the instrument of a certain action or function, which
it performs under certain conditions ; and the concurrence of all
these actions is required for the maintenance of the structure in its
normal or regular state, and for the prevention or the reparation of
those changes, which chemical and physical forces would otherwise
speedily produce in it, from causes hereafter to be explained. Hence
there is a relation oi mutual dependence among the parts of an Organ-
ized structure ; which is quite distinct from that of mere proximity.
Thus, the perfect plant, which has roots, stem, and leaves, is an ex-
ample of an organized structure, in which the relation of the different
parts to the integrity of the whole is sufficiently obvious ; since, when
entirely deprived of either set of them, the plant must perish, unless
it have within itself the power of replacing them.

5. In the lower animals, as in vegetables, we find a marked tend-
ency to the repetition of similar parts, which shows an evident affi-
nity to the mineral kingdom ; and this not only in a composite tree,
or in a coral mass, which, as just stated, must be considered as an
aggregation of distinct individuals; but also in many animals, which
cannot be divided without the destruction of their lives, — especially
among the Radiated, and the lower Articulated tribes. Where such
a repetition exists, some of the organs may be removed without per-
manent injury to the structure ; their function being performed by
those that remain. Thus, it is not uncommon to meet with specimens
of the common five-rayed starfish, in which not only one or two, but
even three or four, of the arms have been lost without the destruction
of the animal's life; and this is the more remarkable, as the arms are
not simply organs of locomotion or prehension, but contain prolonga-
tions of the stomach. In the bodies of the higher animals, however,
where there are few or no such repetitions, and where there is conse-
quently a greater diversity in character and function between the
different organs, the mutual dependence of their actions upon one
another is much greater, and the loss of a single part is much more
likely to endanger the existence of the whole. Such structures are
said to be more highly organized than those of the lower classes ;
not because the whole number of parts is greater, — for it is fre-
quently much less ; but because the number of dissimilar parts, and
the consequent adaptation to a variety of purposes, is much greater,
— the principle of division of labour, in fact, being carried much
further, a much larger class of objects being attained, and a much
greater perfection in the accomplishment of them being thus provided
for.

6. Keeping in view, then, what has just been stated in regard to
the divisibility of a Tree or a Zoophyte into a number of parts, each
capable of maintaining its own existence, we may trace a certain gra-
dation from the condition of the Mineral body to that of the highest
Animal, in regard to the character in question. Thus the individu-

SCIENCE OF PHYSIOLOGY.

34

I

ality of a Mineral substance may be said to reside in each molecule ;
that of a Plant or Zoophyte, in each member; and that of one of the
higher Animals, in the sum of all the organs. The distinction is
much greater, however, between the lowest organized fabric and any
mineral body, than it is between the highest and the lowest organized
structures ; for, as we shall hereafter see, the highest and most com-
plicated may be regarded as made up of an assemblage of the lowest
and simplest ; whose structure and actions have been so modified as
to render them mutually dependent ; but which yet retain a separate
individuality, such as enables them to continue performing their
functions when separated from the mass, so long as the proper con-
ditions are supplied.

7. Between the very simplest organized fabric, and every form of
mineral matter, there is a marked difference in regard to intimate
structure and consistence. Inorganic substances can scarcely be re-
garded as possessing a structure ; since (if there be no admixture of
components) they are uniform and homogeneous throughout, whether
they be existing in the solid, liquid, or gaseous form ; being composed
of similar particles, held together by attractions which affect all alike.
Far different is the character of Organized structures ; for in the
minutest parts of these may be detected a heterogeneous composition, —
a mixture of solid and fluid elements, which are so intimately combined
and arranged, as to impart such peculiarities to the tissues, even in
regard to their physical properties, as we never encounter amongst
Mineral bodies. In the latter, solidity or hardness may be looked
upon as the characteristic condition ; whilst in Organized structures,
softness (resulting from the large proportion of fluid components) may
be considered the distinctive quality, being most obvious in the parts
that are most actively concerned in vital operations. This softness is
evidently connected with the roundness of form characteristic of
organized fabrics, w^hich is most evident when the tissues contain the
greatest proportion of fluid ; whilst the plane surfaces and angular
contours of mineral bodies are evidently due to the mode in which
the solid particles are aggregated together, without any intervening
spaces.

8. The greatest solidity exhibited by Organized fabrics is found
where it is desired to impart to them the simple physical property of
resistance ; and this is attained by the deposition of solid particles,
usually of a mineral character, in tissues that were originally soft and
yielding. It is in this manner that the almost jelly-like substance, in
which all the organs of animals originate, becomes condensed inlo
cartilage, and that the cartilage is afterwards converted into bone ; it
is in the same manner, also, that the stones of fruit, and the heart-
wood of timber-trees, are formed out of softer tissues. But, as we
shall hereafter see, this kind of conversion, whilst it renders the tissue
more solid and durable, cuts it off from any active participation in the
vital operations; and thence reduces it to a state much more nearly
analogous to that of mineral bodies. This resemblance is rendered

22 NATURE AND OBJECTS OF THE

more close by the fact, that the earthy deposits frequently retain a
distinctly crystaline condition ; so that, when they are present in large
proportion, they impart a more or less crystaline aspect to the mass,
and especially a crystaline mode of fracture, which is evident enough
in many shells. It must not be hence concluded, however, that such
substances are of an inorganic nature ; all that is shown by their crys-
taline structure being, that the animal basis exists in comparatively
small amount, and that the mode in which the mineral matter w^as
deposited has not interfered with its crystaline aggregation.

9. It is not to be disputed that a certain degree of homogeneity is
apparently to be found in the minutest elements, into which certain
organized tissues are to be resolved. Thus, in the membranes vf\\\c\i
form the walls of Animal and Vegetable cells^ the highest powers of
the microscope fail in directing any such distinction of fluid and solid
components, as that which has been described as characteristic of
organized structures. Nevertheless it is indubitable that such distinct
components must exist; and this especially from the properties of these
membranes in regard to water. For it is one of the most remarkable
facts in the whole range of science, that a membrane, in which not
the slightest appearance of a pore can be discovered under the highest
powers of the microscope, should be traversed by water ; and that,
too, with no inconsiderable rapidity. The change which these mem-
branes undergo in drying is another proof that they are not so homo-
geneous as they appear, and that water is an element of their structure,
not merely chemically, but mechanically. The same may be said in
regard to the fibres^ which form the apparently ultimate elements of
the simple fibrous tissues in Animals, and which are also met with in
the interior of certain cells and vessels in Plants. These fibres would
appear to be of perfectly simple structure; yet we know from the loss
of fluid, and the change of properties, which they undergo in drying,
that water must have formed part of their substance. — It may be
remarked, however, in regard to both these elementary forms of
organized tissue, that the simplicity of their function is in complete
conformity w^ith the apparent homogeneousness of their structure ; for
the cell-membrane is chiefly destined to act, like the porous septum
in certain forms of the voltaic battery, as a boundary-wall to the con-
tained fluid, without altogether interfering with its passage elsewhere;
the forces which produce its imbibition or expulsion being probably
situated, not in this pervious wall, but in the cavity which it bounds.
And, in the same manner, the function of the fibrous tissues, to which
allusion was just now made, is of an entirely physical character ; being
simply to resist strain or pressure, and yet to allow of a certain degree
of yielding by their elasticity.

10. In all cases in w^hich active vital operations are going on, we
can make a very obvious distinction of the structures subservient to
them, into liquid and solid parts ; and it is, indeed, by the continual
reaction which is taking place between these, that the fabric is main-
tained in its normal condition. For, as we shall hereafter see, it is

SCIENCE OF PHYSIOLOGY. g||

liable to a constant decomposition or separation into its ultimate ele-
ments ; and it is consequently necessary that the matters which have
undergone that disintegration should be carried off, and that they should
be replaced by new particles. These processes of removal and re-
placement, with the various actions subservient to them, make up a
large proportion of the life of all Organized beings. Now as all the
alimentary matter must be reduced to the liquid form, in order that it
may be conveyed to the situations in w^hich it is required, and as all
the decomposed or disintegrated matter must be reduced to the same
form in order to be carried off, the intermingling or mutual penetra-
tion of solids and liquids in the minutest parts of the body is at once
accounted for. We shall hereafter see that a cell^ or closed vesicle,
formed of a membranous wall, and containing: fluid, maybe regarded
as the simplest form of a living body, and tne simplest independent
part or instrument of the more complex fabrics (§ 30).

11. Organized structures are further distinguished from Inorganic
masses, by the peculiarity of their chemical constitution. This pecu-
liarity does not consist, however, in the presence of any elementary
substances, which are not found elsewhere ; for all the elements, of
which organized bodies are composed, exist abundantly in the world
around. It might have been supposed that beings endowed with such
remarkable powers as those of Animals and Plants, — powers which
depend, as we shall hereafter see, upon the exercise of properties to
which we find nothing analogous in the Mineral world, — would have
had an entirely different material constitution ; but a little reflection
will show, that the identity of the ultimate elements of Organized
structures with those of the* Inorganic world, is a necessary conse-
quence of the mode in which the former are built up. For that which
the parent communicates, in giving origin to a new being, is not so
much the structure itself, as the power of forming that structure from
the surrounding elements; audit is by gradually drawing to itself
certain of these elements, that the germ becomes developed into the
complete fabric. Now, of the fifty-jive simple or elementary sub-
stances, which are known to occur in the Mineral world, only about
eighteen or nineteen are found in Plants and Animals ; and many of
these in extremely minute proportion. Some of these appear to be
merely introduced to answer certain chemical or mechanical purposes ;
and the composition of the parts w^hich possess the highest vital en-
dowments, is for the most part simpler and more uniform.

12. The actual tissues of Plants, when entirely freed from the sub-
stances they may contain, have been found to possess a very uniform
composition, and to agree in their chemical properties. The substance
which is left after the action, upon any kind of Vegetable tissue, of
such solvents as are fitted to dissolve out the matters deposited in its
cavities and interstices, is termed Cellulose. It consists of 24 Carbon,
21 Hydrogen, and 21 Oxygen ; or, in other words, of Carbon united
to the elements of w^ater, in the proportion of eight of the former to
seven of the latter. It may be very easily converted into gum or

24 NATURE AND OBJECTS OF THE

sugar, by Chemical processes, which effect the removal or the addi-
tion of the elements of water. Now there is no compound known to
exist in the Inorganic world, which bears the remotest analogy to this ;
and we have no reason to believe that it could be produced in any
other way, than by that peculiar combination of forces which exists in
the growing Plant.

13. In like manner, a large proportion of the Animal tissues, espe-
cially those most actively engaged in the operations of nutrition, have
a nearly uniform composition, when freed from the substances they
contain. We may distinguish among them two chiei proximate prin-
ciples, which appear under various modifications in a great variety of
dissimilar parts, and which seem capable of conversion into other
principles by the addition or subtraction of some of their constituents.
The first and most important of these, named Proteine, consists of 40
Carbon, 31 Hydrogen, 5 Nitrogen, and 12 Oxygen ; and although its
composition is so complex, it appears to act like a simple body, in
uniting with Oxygen, Acids, &c., in definite proportions, as well as
with Sulphur and Phosphorus; — with which last, indeed, it is always
found combined, in the Albumen, Fibrin, &c., that are commonly
regarded as the organic constituents of the Animal tissues. The
second of the chief proximate principles, termed Gelatine, is largely
diffused through the Animal body ; but there is much uncertainty
whether it exists in a condition that can be properly termed organized,
or whether it is a mere deposit, possessing a definite form, like many
of the deposits in the Vegetable tissues. It consists of 13 Carbon,
10 Hydrogen, 2 Nitrogen, and 5 Oxygen; and it is principally cha-
racterized by its solubility in hot water; and by the insolubility of its
compound with tannic acid.

14. We shall hereafter dwell more in detail upon the Chemical
Constitution of the Animal tissues and products (Chap. III). These
substances are only noticed here, in illustration of the general state-
ment, that the proximate principles of Animal and Vegetable bodies, —
that is, the simplest forms to which their component structures can
be reduced, without altogether separating them into their ultimate
elements, — are of extremely peculiar constitution ; being made up of
three elements in Plants, or four in Animals; of which the atoms do
not seem to be united two by two, or by the method of binary com-
position; but of which a large number are brought together to form
one compound atom, of ternary or quaternary composition. This com-
pound atom, like Cyanogen, and many others derived from Organic
products, acts like a simple or elementary one in its combinations
with other substances. It is worthy of remark that, in this respect
as in others, the Vegetable kingdom is intermediate between the
Animal and the Mineral. For the two bases of the Animal tissues,
whose composition has been just given, are remarkable not only for
containing ybwr elements, but for the very large number of atoms of
each which enter into the single compound atom of the Proteine or
Gelatine ; and the proportions of these elements to each other are not

SCIENCE OF PHYSIOLOGY. 39^

such, as to lead to the suspicion that the compound atom may be
regarded as made up of simpler ones, united together in the manner of
the acids and bases of Inorganic Chemistry. On the other hand, the
Cellulose of Plants is much simpler in its composition, since it
includes only three elements, and the numbers which represent their
proportions are smaller; whilst these proportions are themselves such,
as suggest the idea of simplicity in their method of combination, — the
union of water and carbon in the common binary method. This idea
is confirmed by the mode of the original production of cellulose, which
indicates a direct union of carbon with water; as well as by the fact,
that the chemical difference between cellulose and numerous other
substances found in Plants, may be represented by the simple addition
or subtraction of a certain number of atoms of water ; and that the
chemist can effect an actual conversion of the former into certain of
the latter, by means which are calculated to effect such an addition
or subtraction.

15. We shall hereafter see that Vegetables are intermediate be-
tween the Animal kingdom and the Inorganic world in another most
important particular — the nature of the Chemical operations they
effect ; for, although their own organized tissues uniformly have the
composition of Cellulose, they nevertheless have the power of secret-
ing and storing up, in the interstices of these tissues, compounds
which are nearly or exactly identical with animal Proteine in com-
position and properties: and they derive the materials for these com-
pounds— the quaternary as well as the ternary — directly from the
Inorganic world ; being endowed with the wonderful power of elabo-
rating them from the carbonic acid, water, and ammonia, supplied by
the atmosphere and by the soil in which they are implanted. On the
other hand, Animals possess no such power; they are entirely de-
pendent upon Plants for their alimentary materials ; and they employ
for the building-up of their own structures, not the tissues of Plants,
but the substances secreted by them.

2. Of Vital Actions.

16. We are now arrived at the second head of our inquiry, —
namely the nature of those actions, which distinguish living beings
from masses of inert matter, and which are designated as Vital, to
point out their distinctness from Physical and Chemical phenomena.
There can be no doubt whatever, that, of the many changes which
take place during the life, or state of vital activity, of an Organized
being, and which intervene between its first development and its
final decay, a large proportion are effected by the agency of those
forces, which operate in the Inorganic world ; and there is no neces-
sity whatever for the supposition, that these forces have any other
operation in the living body than they would have out of it under
similar circumstances. Thus the propulsion of the blood by the
heart through the large vessels, is a phenomenon precisely analogous

26 NATURE AND OBJECTS OF THE

to the propulsion of any other liquid through a system of pipes by
means of a forcing pump ; and if the arrangement of the tubes, the
elasticity of their walls, the contractile power of the heart, and the
physical properties of the fluid, could be precisely imitated, the arti-
ficial apparatus would give us an exact representation of the actions
of the real one. The motor force of the muscles upon the bones,
again, operates in a mode that might be precisely represented by an
arrangement of cords and levers ; the peculiarity here, as in the for-
mer case, being solely in the mode in which the force is first gene-
rated. So, again, the digestive operations which take place in the
stomach are capable of being closely imitated in the laboratory of the
chemist: when the same solvent fluid is employed, and the same
agencies of heat, motion, &c., are brought into play. Moreover we
shall hereafter see reason to believe, that the peculiar form of Capillary
Attraction, to which the term Endosmose is applied, performs an
important part in the changes which are continually taking place in
the living body.

17. But after every possible allowance is made for the operation
of Physical and Chemical forces, in the living Organism, there still
remain a large number of phenomena, which cannot be in the least
explained by them, and which we can only investigate with success,
when we regard them as resulting from the agency of forces as dis-
tinct from those of Physics and Chemistry, as they are from each
other. It is to these phenomena that we give the name of Vital; the
forces from whose operation we assume them to result, are termed
vital forces ; and the properties, which we must attribute to the sub-
stances exerting those forces, are termed vital properties. Thus we
say that the act of contraction in a Muscle is a vital phenomenon ; be-
cause its character appears totally distinct from that of a Physical or
Chemical action ; and because it is dependent upon other vital changes
in the muscular substance. The act is the manifestation of a certain
force^ the possession of which is peculiar to the muscular structure,

and which is named the Contractile force. Further, that force may
remain (as it were) dormant in the muscular structure, not manifest-
ing itself for a great length of time, and yet capable of being called
into operation at any moment; and this dormant force is termed a
property ; thus we regard it as the essential peculiarity of living Mus-
cular tissue, that it possesses the vital property of Contractility. Or,
to reverse the order, the muscle is said to possess the property of
Contractility ; the property called into operation by the appropriate
stimulus gives rise to the Contractile Force ; and the Force, produces,
if its operation be unopposed, the act of Contraction.

18. It may be said that the distinction here made is a verbal one ;
and that a very simple thing is thus made complex : but it will be
presently seen that it is necessary, in order to enable us to take cor-
rect views of the nature of Vital phenomena, and to understand their
analogies with those of the Inorganic world. And, in fact, the dis-
tinction between the property ^ the force^ and the action^ becomes ap-

SCIENCE OF PHYSIOLOGY. gfJT

parent upon a little consideration. Of the property we are altogether
unconscious, so long as it is not called into exercise ; we could not,
for example, determine by the simple exercise of any of our senses,
whether a certain piece of muscle retained, or had lost its contrac-
tility. When the property is called into action by its appropriate
stimulus, we may convince ourselves that a force is generated, even
if no sensible action is prevented; thus, if we were to hold the two
extremities of a muscle so firmly, as to prevent them from approxi-
mating in the least degree when its contractility was excited, we
should be conscious of a powerful force tending to draw our hands
together ; and we might measure the amount of that force, by me-
chanical means adapted to determine the weight it would sustain.
And lastly, if no obstacle be interposed to the act of Contraction, it
then becomes obvious to our senses, by the change in the shape of
the muscle, and by the approximation of its two extremities, as well
as of the bodies to which they are attached.

19. The advantage of this method of viewing the phenomena of
Life is best shown, by turning our attention for a moment to the
mode of investigation practised in Physics and Chemistry. Thus,
when a stone falls towards the earth, we say that this is an act or
phenomenon of Gravitation. The force with which the stone tends
to fall to the ground, whether it actually falls or not, is called the
force of Gravitation ; and the property, by the exercise of which that
force is generated, is called the property of Gravitation. Now, from
observation of the moon's motion it is shown that she too descends
towards the earth by an act of Gravitation ; and that she does so with
a certain force, which, acting in conjunction with her tangential or
centrifugal force, produces her movement in an elliptical orbit round
the earth ; which force is the result of the exercise of her property of
Gravitation. Could we conceive the Earth to be withdrawn, or an-
nihilated, the property of Gravitation would still exist in the stone,
or in the Moon's mass ; but the force would be extinct, for want of
the excitement of the property ; and the action would consequently
not take place. — Now, it may be further established from Astronomi-
cal observation, that not only does the Moon gravitate towards the
Earth, but the Earth gravitates towards the Moon; so that, if the two
bodies were entirely free from the action of all other forces, they
would fall towards each other (the distance traversed by each being
in proportion to the size of the other), and would meet in their com-
mon centre of Gravity. Hence it is evident that the attractive force
is similar in both bodies ; and our idea of the property of Gravitation
must be extended, therefore, from the Earth to the Moon. Again,
we find ample reason to believe that the same force acts between
the Sun and the Planets, — between the Planets and the Sun, — and
amongst the Planets themselves ; and further, careful experiment
shows that masses of matter upon the Earth's surface are not only
attracted by it, and attract it in their turn, but that they attract and are
attracted by each other. Hence we arrive at the idea of the univer-

28 NATURE AND OBJECTS OF THE

sality of this property of mutual attraction ; and we perceive that, in
spite of the varieties in the actions it produces, and of the differences
in the amounts of the forces to which it gives rise, the property is the
same throughout ; so that we can predict all these actions, and anti-
cipate the forces which will be developed, from the simple general
expression of the property of Mutual Attraction, and of the conditions
according to which it operates, — constituting the Law of Gravitation
or Mutual Attraction.

20. Now in this case of Mutual Attraction, we have no opportu-
nity of witnessing the dormant condition of the property in any mass
of matter ; for, as nothing is wanting but the presence of another
mass to call this property into operation, it is always generating force,
and giving rise to actions. If we could conceive of the existence of
but a single mass of matter in the universe, we shall at once see that,
though possessed of the property of mutual attraction, it would not be
able to exercise it so as to generate an attractive force, or to produce
a movement.

21. But we will turn to another case; in which there is a closer
analogy to the condition of living beings ; and by which, therefore,
the view here put forth may be more clearly illustrated. When a
magnet (itself a bar of iron, having no peculiarity of appearance),
draws towards it a piece of iron, we may say that a Magnetic action
or phenomenon takes place ; further, we speak of the power which pro-
duces the movement, as the Magnetic force ; and we attribute this
force to a certain property inherent in the Magnet, by virtue of which
it draws towards itself all pieces of iron that are within the sphere of
its operation, — and we speak of the iron bar as endowed with the
property of Magnetic attraction. Now we cannot ascertain the pre-
sence or absence of this property in a certain bar of iron, by any dif-
ference in its aspect, its specific gravity, its chemical properties, nor,
in fact, by any other mode than the putting it in circumstances adapted
to call the Magnetic property into action if it really exist ; thus we dip
it into iron filings, and judge by their adhesion whether it is capable
of attracting them ; or, as a still more delicate test, we ascertain whe-
ther it is capable of exerting any repulsive power on a delicately-
suspended needle already magnetized. Again, a needle, or bar of
iron, which exhibits this magnetic power of attracting other portions
of the same metal, exhibits another power which would seem at first
sight totally distinct ; namely, that of constantly turning one of its
extremities towards the north, and the other towards the south, when
it is so supported as to be free to do so. And yet there is no doubt
whatever, that this directing power is only another manifestation of
the same magnetic attractiveness ; depending on the relation between
the magnetized bar, or needle, and the Earth, which must itself be
regarded as a great magnet. Hence the idea of a peculiar kind of
mutual attractiveness, — existing in a limited class only of bodies,
capable of being excited in one by a certain agency on the part of the

SCIENCE OF PHYSIOLOGY. 29

other,* — and requiring for its exercise or manifestation a certain set
of conditions, without which no phenomenon results, — is that which
we regard as fundamental in the Science of Magnetism.

22. We may now turn from these departments of Physical Science
to Chemistry; and here we shall find that the investigation is carried
on upon the very same plan. In fact, the whole science of Chemistry
is founded upon the idea of a certain attractiveness or affinity existing
among the ultimate particles or molecules of the different elementary
substances ; and therefore entirely distinct from the homogeneous at-
traction which holds together the particles of the same mass, or from
the gravitative attraction, which operates alike upon all masses, what-
ever be their composition. Thus we say that Sulphuric acid and Pot-
ash have an affinity for each other; because they unite when they are
brought together, and form a new compound. This is a Chemical action
or phenomenon. Now we know that they tend to unite with a cer-
tain ybrce; a force, however, which cannot be measured mechanically,
and which can only be expressed by comparing it with some other
force of the same kind. Thus we say that the mutual affinity of Sul-
phuric acid and Potash is greater than that of Nitric acid and Pot-
ash ; because, if we pour Sulphuric acid upon Nitrate of Potash, the
Sulphuric acid detaches (as it were) the Potash from its connection
with the Nitric acid, forms a new compound with it, and sets the
Nitric acid free. Hence we say that it is a property of Sulphuric
acid to have a very strong affinity for Potash. This property exists
in every particle of Sulphuric acid that exists, whether free or com-
bined ; but it remains dormant, until it is called into operation by the
contact of Potash ; and it then develops a force, which may com-
pletely change the combinations previously existing, and give rise to
new ones.

23. Now of this property we are not informed by any of the other
properties of Sulphuric acid ; and we only recognize its existence by
the action which is the result of its exercise. If a new element or
compound be discovered, the chemist is totally unable to predict its
force of affinity for this or that substance ; and he can only guess by
analogy, what will be its behaviour under various circumstances.
Thus if it have the external properties of a Metal, he presumes that
it will correspond with the Metals in possessing a strong affinity for
oxygen, sulphur, &c.; whilst if it seem analogous to Iodine, Chlorine,
&c., he infers that it will be a suppprter of combustion, that it will form
an acid with hydrogen, and so on. But even though such guesses may
be made with a certain amount of probability, nothing but experience
can show the positive degrees of affinity, which the substance may
have for others of different kinds ; and the experimental determina-
tion can only be made by observing the actions of the body when
placed in different circumstances, from which we judge of its pro-

* As when one magnet ismade by another; or when iron rails, pokers, &c., become
magnetic by the influence of the earth.

30 NATURE AND OBJECTS OF THE

perties, and of the forces to which these properties give rise when
they are called into operation.

24. It is hoped that the propriety of the distinct use of the terms
vital action, vital force, and vital property , will now be evident ; and
that the student will be now prepared to attach distinct ideas to each
of them. It is the business of the Physiologist to study those actions
or phenomena which are peculiar to living beings, and which are hence
termed vital; he endeavours to trace them to the operation of the fun-
damental properties of organized structures — ^just as the Astronomer
traces all the movements, regular and perturbed, of the heavenly bodies
to the mutual attraction of their masses, acting concurrently with
their force of onward rectilinear movement; or as the Chemist attri-
butes the different acts of combination or separation, which it is his
province to study, to the mutual affinities of the substances concerned :
and the physiologist, like the astronomer or the chemist, seeks to de-
termine the laws according to which these properties act, or, in other
words, to express the precise conditions under which they are called
into play, and the forces which they then generate. It is only in this
manner, that Physiology can be rightly studied and brought to the
level of other sciences. There can be no doubt that its progress has
been greatly retarded by the assumption that its phenomena were all
to be attributed to the operation of some general controlling agency, or
Vital Principle; and that the laws expressing the conditions of these
phenomena must be sought for by methods of investigation entirely
distinct from those which are employed in other sciences. But a
better spirit is now abroad ; and the student cannot be too strongly
urged to discard any ideas of this kind as absolutely untenable; and
to keep steadfastly in view, that the laws of Vital Action are to be at-
tained in the same manner as those of Physics or Chemistry, — that is,
by the careful collection and comparison of vital phenomena, and by
applying to them the same method of reasoning, as that which is used
in determining the forces and properties on which other phenomena
depend. True it is, that we can scarcely yet hope to reach the same
degree of simplification, as that of which other sciences are capable;
and this on account of the very complex nature of the phenomena
themselves, and the difficulty of satisfactorily determining their con-
ditions. The uncertainty of the results of Physiological experiments
is almost proverbial ; that uncertainty does not result, however, from
any want of fixity in the conditions under w^hich the vital properties
operate, but merely from the influence of differences in those condi-
tions, apparently so slight as to elude observation, and yet suflficiently
powerful to produce an entire change in the result. And, owing to
that mutual dependence of the different actions of the organized
structure, to which reference has been already made (§ 5), we cannot
seriously derange one class of these actions, without also deranging,
or even suspending others; — a circumstance which obviously renders
vital phenomena much more difficult of investigation than those of
inorganic matter.

SCIENCE OF PHYSIOLOGY. 31

25. All sciences have their " ultimate facts ;" that is, facts for which
no other cause can be assigned than the Will of the Creator. Thus,
in physics, we cannot ascend above the fact of Attraction (which ope-
rates according to a simple and universal law) between all masses of
matter ; and in chemistry, we cannot rise beyond the fact of Affinity
(limited by certain conditions which are not yet well understood)
between the particles of different kinds of matter. When we say
that we have explained any phenomenon, we merely imply that we
have traced its origin to these properties, and shown that it is a ne-
cessary result of the laws according to which they operate. For the
existence of the properties, and the determination of the conditions,
we can give no other reason than that the Creator willed them so to
be ; and, in looking at the vast variety of phenomena to which they
give rise, we cannot avoid being struck with the general harmony
that exists amongst them, and the mutual dependence and adaptation
that may be traced between them, when they are considered as por-
tions of the general economy of Nature. — There is no difference in
this respect between Physiology and other sciences; except that the
number of these (apparently) ultimate facts is at present greater in
physiology, than it is in other sciences, because we are not at present
able to include them under any more general expression. Thus we
find a certain peculiar endowment existing in one form of structure ;
and another endowment, equally peculiar, inherent in another; but
we can give no reason why the structure called muscular, should
possess contractility, and w'hy the structure called nervous should be
capable of generating and conveying the force which excites that
contractility to action. Each of these facts, therefore, is for the pre-
sent the limit to our knowledge ; we can ascertain the conditions,
according to which the muscular contractility, and the exciting powder
of the nerve, are called into operation, and can form some estimate
of the amount of the forces which they generate ; but we cannot see
clearly that they are necessarily connected by any common tie, such
as that which binds together the planetary masses, at the same time
that it weighs down the bodies on the surface of the earth towards its
centre.

26. The present condition of Physiology, however, finds its parallel
in the history of some other sciences, in which there was an equal
number of such facts that were for a time regarded as ultimate. Thus,
until the phenomena of Terrestrial Magnetism had been investigated,
the polar direction of the magnetic needle, its dip, and its variation,
were regarded as phenomena altogether distinct from the phenomena
of attraction and repulsion w^hich are exhibited between two magnets ;
and the former seemed " ultimate facts," of which no further account
could be given. So, also, before the time of Newton, the movements
of celestial and terrestrial bodies were supposed to be entirely desti-
tute of connection with each other. But, as the knowledge of the
Earth's Magnetism has shown that the direction, variation, and dip
of the compass are referable to the very polar forces which show

32 NATURE AND OBJECTS OF THE

themselves on a small scale when two magnets are brought near each
other ; and as the mutual attraction of the earth and moon, of the sun
and planets, has been shown to result from the same property, as that
which draws together any two masses that are freely suspended ; so
may it be fairly anticipated that an increased attention to vital phe-
nomena, and a more philosophical method of reasoning upon them,
will tend towards the same kind of generalization, and, therefore, to
the simplification of the principles of the science.

27. To satisfy ourselves — as some have done — with attributing
the phenomena of Life to the agency of a " Vital Principle," is cer-
tainly a very easy way of extricating ourselves from the difficult path
of physiological inquiry. But we are not in that manner conducted
one step nearer to the object of that inquiry. For it is just as if, after
the manner of the Ancients, we were to attribute the movements of
the heavenly bodies to a " principle of motion," without inquiring
into the conditions according to which it acts. Now, as Modern
Physics show that all these varied movements (so different in kind,
that no two of the heavenly bodies move at the same rate, or in paths
of similar curvature), are the results of two forces, each acting accord-
ing to its own laws, and modifying the other ; and as it refers these
forces to the exercise of simple properties of matter ; so should the
Physiologist seek for the common sources of the phenomena he wit-
nesses, and for the properties of the organized structures, by the
exercise of which they are produced. These properties do not differ
more from those which he elsewhere encounters, than organized
fabrics differ from masses of inorganic matter, both in structure and
composition ; and there is no necessity, therefore, to call in the aid
of any other agency, to account for the peculiar endowments of those
fabrics.

28. The advocates of the existence of a separate Vital Principle,
as the unknown cause of the phenomena of life, rely much upon the
peculiar adaptation, which may be observed amongst the several
actions of an organized being ; and upon their common subserviency
to the maintenance of the integrity of the structure, and to the repara-
tion of the effects of disease or injury, which imparts to them a cha-
racter of unity that seems to be wanting elsewhere. But if we take
a general survey of the phenomena of the universe at large, we shall
find the adaptation just as complete, the mutual dependence as close,
the unity of the whole as perfect. And as the Philosopher can do
nought else than attribute this harmony, this mutual adaptation and
dependence, this unity of purpose, in the phenomena of the Macro-
cosm or Universe, to the Infinite VV'isdom and Power of the Design-
ing Mind, so must he depart from all right methods of reasoning, to
suppose that the like harmony, adaptation, and unity in the operations
of the Microcosm^ or little world in his own body, can have any other
source.

29. The only sense in which the term "Vital Principle" can be
properly used, is as a convenient and concise expression for the sum

SCIENCE OF PHYSIOLOGY. 33

total (so to speak) of the powers which are developed by the action
of the Vital properties of Organized structures — these being not yet
fully understood, and the conditions of their action being but imper-
fectly known. In this manner it has been customary to talk of the
principles of Gravity, of Electricity, of Magnetism, &c., as the un-
known causes of certain phenomena, which seemed to be connected
by the same general conditions; but as the advance of Physical sci-
ence has done away with these modes of expression, by referring all
the phenomena to the simple properties of matter, and by fixing the
conditions under which they occur, so should we aim at a corre-
sponding simplification and precision in Physiology. The use of a
term like Vital Principle, even in the restricted sense now specified,
is attended with this danger: — that it rather checks inquiry, by giving
rise to the idea that a reference to the agency of such a principle is
alone sufficient to explain the phenomena ; and, as it is attended wdth
no corresponding advantage, it seems preferable to discard the term
altogether. It will not be again introduced, therefore, in this Trea-
tise ; the object of which is to place the student in possession of
what has been ascertained regarding the peculiar or vital properties
of Organized Tissues. This may be most advantageously effected,
by first making him acquainted with the general history of the series
of phenomena exhibited by Living Beings of the simplest character,
and by then tracing these phenomena, so far as possible, to their hid-
den sources. For this purpose w^e must have recourse to the sim-
plest forms of Cryptogamic Plants, which consist of mere aggrega-
tions of cells, every one of which may be regarded as a distinct indi-
vidual, since it is perfectly independent of the rest, and performsybr
and by itself, all the functions of Growth and Reproduction. We
shall find, then, in the operations of the simple cell, an epitome, as it
were, of those of the highest and most complex Plant ; whilst those of
the higher Plants bear a close correspondence
with those which are immediately concerned
in the Nutrition and Reproduction of the Ani-
mal body. The functions peculiar to Animals,
and distinguishing them from Plants, must be
separately considered.

30. A Cell, in Physiological language, is a
closed vesicle or minute bag, formed by a
membrane, in w^hich no definite structure can
be discerned, and having a cavity, which may ^. , . , . , „

' 'IT • o 1 Simple isolated cells, con-

contam matters of variable consistence, ouch taining reproductive moie-
a cell constitutes the whole organism of such

simple plants as the Protococcus vivalis (Red Snow), or Palmella
cruenta (Gory Dew); for although the patches of this kind of vege-
tation which attract our notice, are made up of vast aggregations of
such cells, yet they have no dependence upon one another, and the
actions of each are an exact repetition of those of the rest. In such
a cell, every organized fabric, however complex, originates. The
3

34 NATURE AND OBJECTS OF THE

vast tree^ almost a forest in itself, and the feeling, thinking, intelli-
gent man^ spring from a germ, that differs in no obvious particular
from the permanent condition of one of these lowly beings. But
whilst the powers of the latter are restricted, as we shall see, to the
continual multiplication of new and distinct individuals like itself,
those of the former enable it to produce new cells that remain in
closer connection with each other; and these are gradually converted,
by various transformations of their own, into the diversified elements
of a complex fabric. The most highly organized being, however,
will be shown to consist in great part of cells that have undergone
no such transformation, amongst which the different functions per-
formed by the individual in the case just cited, are distributed, as it
were ; so that each cell has its particular object in the general eco-
nomy, whilst the history of its own life is essentially the same as if it
were maintaining a separate existence.

31. We shall now" examine, then, the history of the solitary cell of
the Red Snow% or of any other equally simple plant, from its first
development to its final decay; in other words, we shall note those
Vital Phenomena, w^hich are as distinct from those of any inorganic
body, as is its organized structure (simple as it appears) from the
mere aggregation of particles in the inert mass. In the first place,
the cell takes its origin from a germ, which is a minute molecule, that
cannot be seen without a microscope of high power. This molecule
appears, in its earliest condition, to be a simple homogeneous par-
ticle, of spherical form; but it gradually increases in size ; and a dis-
tinction becomes apparent between its transparent exterior and its
coloured interior. Thus we have the first indication of the cell-wall,
and the cavity. As the enlargement proceeds, the distinction be-
comes more obvious; the cell-wall is seen to be of extreme tenuity
and perfectly transparent, and to be homogeneous in its texture;
whilst the contents of the cavity are distinguished by their colour,
which is bright-red in the species just mentioned, but more com-
monly green. At first they, too, seem to be homogeneous; but a
finely granular appearance is then perceptible ; and a change gradu-
ally takes place, which seems to consist in the aggregation of the
minute granules into molecules of more distinguishable size and form.
These molecules, which are the germs of new cells, seem to be at
first attached to the wall of the parent-cell ; afterwards they separate
from it and move about in its cavity; and at a later period, the
parent-cell bursts and sets them free. Now, this is the termination
of the life of the parent-cell; but the commencement of a life of a
new^ generation ; since every one of these germs may become de-
veloped into a cell, after precisely the foregoing manner, and will
then in its turn propagate its kind by a similar process.

32. By reasoning upon the foregoing history, we may arrive at cer-
tain conclusions, which will be found equally applicable to all living
beings. In the first place, the cell originates in a germ or reproduc-
tive molecule, which has been prepared by another similar cell that

SCIENCE OF PHYSIOLOGY. 35

previously existed. There is no sufficient reason to believe, that
there is any exception to this rule. So far as we at present know,
every Plant and every Animal is the offspring of a parent, to which
it bears a resemblance in all essential particulars; and the same may
be said of the individual cells, of which the Animal and Vegetable
fabrics are composed. But how does this germ^ this apparently homo-
geneous molecule, become a Cell ? The answer to this is only to be
found in its peculiar property of drawing materials to itself from the
elements around, and of incorporating these with its own substance.
The Vegetable cell may grow wherever it can obtain a supply of
Water and Carbonic acid ; for these compounds supply it with Oxy-
gen, Hydrogen, and Carbon, in the state most adapted for the exer-
cise of the combining power, by which it converts them into that
new compound, whose properties adapt it to become part of the
growing organized fabric. Here, then, we have two distinct opera-
tions ; — the union of the Oxygen, Hydrogen and Carbon, into that
gummy or starchy product, which seems to be the immediate ■pabulum
of the Vegetable tissues ; — and the incorporation of that product with
the substance of the germ itself.

33. The^r5^ of these changes may Z>e, and probably ^5, of a purely
Chemical nature ; and analogous cases are not wanting, in the pheno-
mena of Inorganic Chemistry, in which one body, a, exerts an influ-
ence upon two other bodies, b and c, so as to occasion their separa-
tion or their union, without itself undergoing any change. Thus
Platinum, in a finely-divided state, will cause the union of Oxygen
and Hydrogen at ordinary temperatures; and finely-powdered Glass
will do the same at the temperature of 572°. This kind of action is
called Catalysis. A closer resemblance, perhaps, is presented by the
act oi fermentation ; in which a new arrangement of particles takes
place in a certain compound, by the presence of another body which
is itself undergoing change, but which does not communicate any of
its elements to the new products. Thus, if a small portion of animal
membrane, in a certain stage of decomposition, be placed in a solu-
tion of sugar, it will occasion a new arrangement of its elements,
which will generate two new products, alcohol and carbonic acid. If
the decomposition of the membrane have proceeded further, a differ-
ent product w^ill result; for instead of alcohol, lactic acid will be
generated. There appears no improbability, then, in the idea, that
the influence exerted by the germinal molecule is of an analogous
nature; and that it operates upon the elements of the surrounding
water and carbonic acid, according to purely Chemical laws, uniting
the Carbon with the elements of Water, and setting free the Oxygen.
This result of the nutritive operations of the simple cellular plants
may be easily verified experimentally, by exposing the green scum,
which floats upon ponds, ditches, &c., and which consists of the
cells of a minute Cryptogamic Plant, to the influence of light and
warmth beneath a receiver; it is found that oxygen is then liberated,
by the decomposition of the carbonic acid contained in the water.

36 NATURE AND OBJECTS OF THE

We shall presently have to return to the consideration of the Chemi-
cal phenomena of living beings; and shall pass on, therefore, to con-
sider those to which no such explanation applies.

34. The second stage in the nutritive process consists in the appro-
priation of the new product thus generated to the enlargement of the
living cell-structure; — a phenomenon obviously distinct from the pre-
ceding. It is well to observe, that this process, which constitutes the
act of organization, may be clearly distinguished in the higher Plants
and Animals, as consisting of two stages ; the first of these being the
further preparation or elaboration of the fluid matter, by certain altera-
tions whose nature is not yet clear, so as to render it organizable, or
fit to undergo organization ; the second being the act of organization
itself, or the conversion of the organizable matter into the solid text-
ure, and the development in it of the properties that distinguish that
texture. Thus, for example, we do not find that a solution of dex-
trin (or starch-gurn) is capable of being at once applied to the deve-
lopment of vegetable tissue, although it is identical in composition
with cellulose ; for it must first pass through a stage, in which it pos-
sesses a peculiar glutinous character, and exhibits a tendency to spon-
taneous coagulation, that seems like an attempt at the production of
organic forms. And in like manner the albumen of Animals is evi-
dently not capable of being applied to the nutrition of the fabric, until
it has been first converted into fibrin ; which also is distinguished by
its tenacious character, by its spontaneous coagulability, and by the
fibrous structure of the clot. Now, in both these cases, there is pro-
bably some slight modification in Chemical composition, that is, in
the proportions of the ultimate elements; but the principal alteration
is evidently that which is eflfected by the re-arrangement of the con-
stituent particles; so that, without any considerable change in their
proportions, a compound of a very diflferent nature is generated. Of
the possibility of such changes, we have abundant illustrations in
ordinary Chemical phenomena ; for there is a large class of sub-
stances, termed isomeric, which, with an identical composition, pos-
sess chemical and physical properties of a most diverse character.

35. But we cannot attribute the production of Fibrin from Albu-
men, the organizable from the unorganizable material, to the simple
operation of the same agencies as those which determine the produc-
tion of the different isomeric compounds; for the properties of Fibrin
are much more vitally distinct from those of Albumen, than they are
either chemically or physically ; that is, we find in the one an inci-
pient manifestation of Life, of which the other shows no indications.
The spontaneous coagulation of fibrin, which takes place very soon
after it has been withdrawn from the vessels of the living body, is a
phenomenon to which nothing analogous can be found elsewhere ; for
it has been clearly shown not to be occasioned by any mere physical
or chemical change in its constitution ; and it takes place in a man-
ner which indicates that a new arrangement of particles has taken
place in it, preparatory to its being converted into a living solid. For

(

SCIENCE OF PHYSIOLOGY. 37.

this coagulation is not the mere homogeneous settings which takes
place in a solution of gelatine in cooling, nor is it the aggregation of
particles in a mere granular state, (closely resembling that of a che-
mical precipitate), which takes place in the coagulation of albumen:
it is the actual production of a sim^Xe fibrous tissue^ by the union of
the particles of fibrin in a determinate manner, bearing a close resem-
blance to the similar process in the living body (§ 188). We say,
then, that the coagulation of Fibrin, and the production of a fibrous
tissue, are the result of its vital properties, rather than of chemical or
physical agencies; because no substance is known to perform any
such actions, without having been subjected to the influence of a liv-
ing body; and because the actions themselves are altogether different
from any which we witness elsewhere. This production of an organ-
izahle or partially vitalized substance, from an unorganizable one,
possessing none but chemical properties, and therefore as yet inert^
so far as the living body is concerned, may be termed Assimilation ;
and it may be conceived, as we have seen, to consist of a new
arrangement of the particles of the substance thus changed, analo-
gous to that which occurs when one isomeric product is converted
into another by some ordinary chemical agency, — Heat or Electricity
for example ; but not ideiitical with it, because it cannot be produced
by any other agency than that furnished by a living structure.

36. We now come to the act of Organization itself; which seems
to consist of a continuation of the same kind of change, — that is, a
new arrangement of the particles, producing substances which differ
both as to structure and properties from the materials employed, but
which maybe so closely allied to them in chemical composition, that
the difference cannot be detected. Thus, from the dextrin of plants
is generated, in the process of cell-development, the cellulose which
constitutes the walls of the cells : chemically speaking, there seems
to be no essential distinction between these two substances ; and yet
between the living, growing, reproducing cell, and the inert, un-
changing starch-grain, how wide the difference ! So in the animal
body, we find that the composition of the fibrin of muscular fibre
scarcely differs, in regard to the proportion of its elements, from the
fibrin, or even from the albumen, of the blood; and yet what an en-
tire re-arrangement must take place in the particles of either, before
a tissue so complex in structure, and so peculiar in properties, as
muscular fibre, can be generated!

37. Both in the Plant and the Animal, we find that tissues present-
ing great diversities both in structure and properties, may take their
origin in the same organizable material ; but in every case (at least
in the ordinary processes of growth and separation) the new tissue of
each kind is formed in continuity with that previously existing. Thus
in the stem of a growing tree, from the very same glutinous sap or
cambium, intervening between the wood and the bark, the wood ge-
nerates, in contact with its last-formed layer, a new cylinder of wood;
whilst the bark produces, in contact with its last-formed layer, a new.

38 NATURE AND OBJECTS OF THE

cylinder of bark, — the woody cylinder being characterized by the
predominance of ligneous fibre and ducts, and the cortical by the
predominance of cellular tissue. In like manner we find that, in
animals, muscle produces muscle, bone generates bone, nerve deve-
lops nerve in continuity with it, — all at the expense of the materials
supplied by the very same blood. The JVutrition of tissues, by the
organization of the materials contained in the nutrient fluid with
which they are supplied, may be superficially compared therefore to
the act of crystalization, when it takes place in a mixed solution of
two or more salts. If in such a solution we place small crystals
of the salts it contains, these crystals will progressively increase by
their attraction for the other particles of the same kind, which were
previously dissolved ; each crystal attracting the particles of its own
salt, and exerting no influence over the rest. But it must be borne
in mind, that such a resemblance goes no further than the surface ;
for the growth of a crystal cannot be really regarded as in the least
analogous to that of a cell. The crystal progressively increases by
the deposit of particles upon its exterior ; the interior undergoes no
change ; and whatever may be the size it ultimately attains, its pro-
perties remain precisely the same as those of the original nucleus.
On the other hand, the cell grows from its original germ by a pro-
cess o{ interstitial deposit; the substance of which its wall is composed,
extends itself in every part ; and the new matter is completely incor-
porated with the old.

38. Moreover, as the increase proceeds, we see an evident distinc-
tion between the cell-wall and its cavity ; and we observe that the
cavity is occupied by a peculiar matter, different from the substance
of the cell- wall, though obviously introduced through it. Of the
essential difference which may exist in composition, between the
cell-wall and the contents of the cavity, we have a remarkable exam-
ple in the case of the simple Cryptogamic plant, which constitutes
Yeast, and which differs in no essential part of the history of its growth
from the species already referred to. The substance of its cell-walls
is nearly identical with ordinary Cellulose ; whilst the contents of
the cells are closely allied in composition to Protein, the material of
many Animal tissues. Again, in the fat-cells of Animals, the cell-
wall is formed from a protein compound ; whilst the oily contents
agree, in the absence of nitrogen, and in their general chemical rela-
tions, with the materials of the tissues of Plants. It is evident, then,
that one of the inherent powers of the cell, is that by which it not only
combines the surrounding materials into a substance adapted for the
extension of its wall^ but that which enables it to exercise a similar
combining power on other materials derived from the same source,
and to form a compound, — of an entirely different character, it may
be, — which occupies its cavity. Now this process is as essential to
our idea of a living cell, as is the growth of its wall ; and it must
never be left out of view, when considering the history of its deve-
lopment.

SCIENCE OF PHYSIOLOGY, 3^

39. Every kind of cell has its own specific endowments ; and ge-
nerates in its interior a compound peculiar to itself. The nature of
this compound is much less dependent upon the nutrient materials
which are supplied to the cell, than upon the original inherent powers
of the cell itself, derived from its germ. Thus we find that the Red
Snow and Gory Dew invariably form a peculiar red secretion ; and
that they will only grow where they can obtain, from the air and
moisture around, the elements of that secretion. Again, the Yeast
Plant invariably forms a secretion analogous to animal protein ; and
it will only grow in a fluid which supplies it with the materials of
that substance. Hence the Red Snow would not grow in a ferment-
ible saccharine fluid ; nor would the Yeast Plant vegetate on damp
cold surfaces. Yet there is little diff*erence, if any, between their cell-
walls in regard to chemical composition. — So, also, we shall find
hereafter, that one set of cells in the animal body will draw into
themselves, during the process of growth, the elements of bile ; ano-
ther, the elements of milk ; another, fatty matter, and so on ; — the
peculiar endowments of each being derived from their several germs,
which seem to have an attraction for these substances respectively,
and which thus draw them together ; whilst the cell-wall appears to
have a uniform composition in all instances.

40. The term Secretion, or setting-apart, is commonly applied to
this operation, to distinguish it from Nutrition or growth ; but it is
obvious from what has now been stated, that the act of secretion is
in reality the increase or growth of the cell-contents, just as the pro-
cess of enlargement is the increase or growth of the cell-wall ; and
that the tw^o together make up the whole process of Nutrition, which
cannot be properly understood, unless both are taken into account.
It is to be remembered, however, that the contents of the cell may
not be destined to undergo organization ; indeed we shall find here-
after, that the main use of certain cells is to draw off from the circu-
lating fluid such materials as are incapable of organization ; and the
operation may be so far attributed, therefore, to the agency of Che-
mical forces. But we shall find that, in other instances, the cell-con-
tents are destined to undergo organization, and this either within the
parent-cell, or after they leave it ; here, then, we must recognize a
distinct vitalizing agency, as exerted by the cell upon its contents.

41. This organizing or vitalizing influence must be exerted upon
a certain portion of the contents of every cell that is capable of repro-
ducing itself; for it is in this manner that those germs are produced,
in which all the wonderful properties are inherent, that are destined
to manifest themselves, when they are set free from the parent-cell.
This power of Reproduction is one of those, which most remarkably
distinguishes the living being ; and we shall find that, in the highest
Animal, as in the humblest Plant, it essentially consists in the prepa-
ration of a cell-germ, which, when set free, gradually develops itself
into a structure like that from which it sprang. The reproductive
molecules or cell-germs are formed, like the tissue and the contents

40 NATURE AND OBJECTS OF THE

of the parent-cell, from the nutrient materials which it has the power
of bringing together and combining ; and in their turn they pass
through a corresponding series of changes ; and at length produce a
new generation of similar molecules, by which the race is destined
to be continued. Notwithstanding the mystery which has been sup-
posed to attach itself to this process, it is obvious that there is nothing
in reality more difficult to understand in the fact that the parent-cell
organizes and vitalizes the cellulose which it has elaborated, so that
it should form the germ of a new individual possessing similar pro-
perties with itself, than in its incorporating the same material with
its own structure, and causing it to take a share in its own actions.

42. Finally, the parent-cell having arrived at its full development,
having passed through the whole series of changes which is charac-
teristic of the species, and having prepared the germs by which the
race is to be propagated, dies and decays; — that is, all those opera-
tions, which distinguish living organized structures from inert matter,
cease to be performed ; and it is subject to the influence of chemical
forces only, which speedily occasion a separation of its elements, and
cause them to return to their original forms, namely, water and car-
bonic acid. It must not be hence supposed, however, that there is
anything peculiar in the forces which hold together those elements
during the life of the cell, and that the operation of the ordinary che-
mical agencies is resisted by the superior power of vitality. On the
contrary it is certain that interstitial death and decay are incessantly
taking place during the whole life of the being ; and that the main-
tenance of its healthy or normal condition depends upon the constant
removal of the products of that decay, and upon their continual re-
placement. If, on the one hand, those products be retained, they act
in the manner of poisons ; being quite as injurious to the welfare of
the body, as the most deleterious substances introduced from without.
On the other hand, if they be duly carried off, but be not replaced,
the conditions essential to vital action are not fulfilled, and the death
of the whole must be the result.

43. Now it is to be observed that, as Plants obtain the materials
oi ih^u growth from water and carbonic acid, taking the carbon from
the latter and setting free the oxygen, so do they require, as the con-
dition for their decay, the presence of oxygen, which may unite with
the carbon that is to be given back to the atmosphere. If secluded
from this, the vegetable tissues may be preserved for a long time
without decomposition. Generally speaking, indeed, they are not
prone to rapid decay, except at a high temperature ; and hence it is
that we have so little evidence, in Plants, of the constant interstitial
change, of which mention has just been made. Its existence, how-
ever, (at least in all the softer portions of the structure,) is made evi-
dent by the fact, that a continual extrication of carbonic acid takes
place, to an amount which sometimes nearly equals that of the car-
bonic acid decomposed, and of the oxygen set free, in the act of
Nutrition (§ 33). The latter operation is only effected under the

I

SCIENCE OF PHYSIOLOGY. 41

stimulus of sun-light ; the former is constantly going on, by day and
by night, in sunshine and in shade ; and if it be impeded or prevented
by want of a due supply of oxygen, the plant speedily becomes un-
healthy. Now this extrication of the products of interstitial decay is
termed Excretion. It is usually confined in Plants to the formation
of carbonic acid and water, by the union of the particles of their tis-
sues with the oxygen of the air, — a process identical with that which
occurs after the death of the entire structure. But in Animals it is
much more complicated, owing to the larger number of constituents
in their fabric, and to the much greater variety in the proportions in
which these are combined ; hence the products of interstitial decom-
position are much more numerous and varied, and several distinct
modes are devised for getting rid of them. Moreover, as the animal
tissues are much further removed than the Vegetable from the com-
position of Inorganic bodies, they are subject to much more rapid
and constant decay; and we shall find that this decay is so consider-
able in amount, as to require on the one hand a very complex excre-
tory apparatus to carry off the disintegrated matter, and on the other
a large supply of nutrient material to replace it.

44. The preceding history may be thus summed up. — 1. The Vege-
table cell-germ or reproductive molecule draws to itself, and combines
together, certain inorganic elements; and thereby produces a new and
peculiar compound. This compound, however, exhibits no properties
that distinguish it from others, in which ordinary Chemical agencies
have been concerned ; and we may, therefore, regard the first act of
the cell-germ as of a purely chemical nature. We shall presently see
that chemical agencies are undoubtedly concerned in it, to a very con-
siderable degree. The Animal cell-germ does not possess the same
Chemical power ; it is not capable of decomposing the water, carbonic
acid, and ammonia, which include the elements of its tissues ; and it is
entirely dependent for its growth upon the supply of nutriment pre-
viously prepared for it by the agency of the vegetable kingdom, many
species of which possess, as we have seen, the power of generating a
protein compound within their cells, though they cannot organize it. —

2. The cell-germ then exerts an agency upon the pabulum thus pre-
pared ; by which a new arrangement of its particles is produced.
This new arrangement gives new and peculiar qualities to the fluid,
which show that it is something more than a mere chemical compound,
and that it is in the act of undergoing the process of organization. —

3. The Organization of this elaborated pabulum then takes place:
its materials are withdrawn from the fluid, and incorporated with the
solid texture ; and in thus becoming part of the organized fabric, they
are caused to exhibit its own peculiar properties. — 4. At the same
time another portion of this pabulum is gradually prepared to serve as
the germ of a new cell, or set of cells, by which the same properties
are to be exhibited in another generation. — 5. By a Chemical opera-
tion resembling that concerned in the first preparation of the pabulum,
a certain secretion more or less differing from it in character, but not

42 NATURE AND OBJECTS OF THE

destined to undergo organization, is formed in the cavity of the cell. —
6. A decomposition or disintegration of the organized structure, is
continually going on, by the separation of its elements into simpler
forms, under the influence of purely Chemical agencies; and the setting
free of these products by an act of excretion, is thus incessantly
restoring to the inorganic world a portion of the elements that have
been withdrawn from it. — 7. When the term of life of the parent-
cell has expired, and its reproductive molecules are prepared to con-
tinue the race, the actions of nutrition cease; those of decomposition
go on unchecked ; and the death of the structure, or the loss of its
distinguishing vital properties, is the result. By the decomposition,
which then takes place with increased rapidity, its elements are re-
stored to the inorganic w^orld; presenting the very same properties as
they did when first withdrawn from it; and becoming capable of be-
ing again employed, by any successive numbers of living beings, to
go through the same series of operations.

45. Thus, then, we see that our fundamental idea of the properties
of the simplest living being consists in this : — that it has the capability
of drawing into its own substance certain of the elements furnished by
the inorganic w^orld ; — that it forms these into new combinations
(which the Chemist may find out methods of imitating); — that it re-
arranges the particles of these combinations, in that peculiar mode
which we call organization; — that in producing this new arrangement
it also calls forth or develops in them a new set of properties, which
we call vital, and which are manifested by them, either as connected
with the parent structure, or as appertaining to the germs of new
structures, according to the mode in which the materials are applied ;
— that, notwithstanding its peculiar condition, it remains subject to
the ordinary laws of Chemistry, and that decomposition of its struc-
ture is continually taking place ; — and finally, that the duration of its
vital activity is limited ; the changes which the organic structure un-
dergoes, in exhibiting its peculiar actions, being such as to render it
(after a longer or shorter continuance of them) incapable of any longer
performing them.

46. There is abundant evidence, that the duration of the Life^ or
state of Vital Jlctivity^ of an organized structure, is inversely propor-
tioned to the degree of that activity ; and consequently that Life is
shortened by an increased or abnormal activity; -whilst it may often
be prolonged by influences which diminish that activity. Thus we
shall hereafter find reason to believe, that the duration of life in the
Muscular and Nervous tissues of Animals is entirely dependent upon
the degree in which they are exercised ; every call upon their activity
causing the death and disintegration of a certain part; whilst if they
be allowed to remain in repose for a time, only that amount of decom-
position will take place to which their chemical character renders them
liable. Again, we may trace the connection between the vital activ-
ity of a part and the duration of its life, by comparing the transitory
existence of the leaves of a Plant, which are its active organs of nu-

SCIENCE OF PHYSIOLOGY. 43

trition with the comparative permanence of its woody stem^ the parts
of which, when once completely formed, undergo very little subse-
quent change. The most striking manifestation of this connection,
however, is afforded by that condition in which, without any appre-
ciable amount of vital activity or change, an organized structure may
remain unaltered for centuries ; not only presenting at the end of that
time its original structure, but being prepared to go through its regular
series of vital operations, as if these had never been interrupted.
This state may be designated as Dormant Vitality. It differs, on the
one hand, from Life; because life is a state of Jidivity. On the other
hand, it differs from Death; because Death implies not merely a sus-
pension of activity, but a total loss of vital properties. Now in the
state of Dormant vitality, the vital properties are retained ; but they
are prevented from manifesting themselves by the want of the neces-
sary conditions. When these conditions are supplied, the state of
vital activity is resumed, and all the functions of life go on with
energy.

47. Of this Dormant Vitality it may be well to adduce some ex-
amples ; which may assist in impressing on the mind of the student
the general views here put forth. This condition is manifested in the
most remarkable manner by the seeds and germs of plants : many of
which are adapted to remain, for an unlimited period, in a state of
perfect repose, and yet to vegetate with the greatest activity, as soon
as ever they are subjected to the necessary influence. Thus the
sporules of the Fungi, which can only germinate in decaying organ-
ized matter, seem universally diffused through the atmosphere, and
ready to vegetate with the most extraordinary rapidity, whenever a
fitting opportunity presents itself. This at least appears to be the
only feasible mode of explaining their appearance, in the forms of
Mould, Mildew, &c., on all moist decaying substances; and that there
is no improbability in the supposition itself, is shown by the excessive
multiplication of these germs, a single individual producing not less
than ten millions of them, so minute as when collected to be scarcely
visible to the naked eye, rather resembling thin smoke, and so light
as to be wafted by every movement of the atmosphere ; — so that, in
fact, it is difficult to imagine any place from which they can be ex-
cluded. Moreover it is certain that an equally tenacious vitality exists
in the seeds of higher plants. Those of most species inhabiting tempe-
rate climates are adapted to remain dormant during the winter; and
may be easily preserved, in dry air, and at a moderate temperature,
for many years. Some of those which had been kept in the Herba-
rium of Tournefort during upwards of a century, were found to have
preserved their fertility. Cases are of no unfrequent occurrence, in
which ground that has been turned up, spontaneously produces plants
dissimilar to any in their neighbourhood. There is no doubt that in
some of these cases, the seed is conveyed by the wind, and becomes
developed in spots which afford congenial soil, — as already remarked
in the case of the Fungi. Thus it is commonly observed that clover

44 NATURE AND OBJECTS OF THE

makes its appearance on soils which have been rendered alkaline by
lime, by strewed wood-ashes, or by the burning of weeds. But there
are many authentic facts, which can only be explained upon the sup-
'^josition, that the seeds of the newly-appearing plants have lain for a
long period imbedded in the soil, at such a distance from the surface
as to prevent the access of air and moisture ; and that, retaining their
vitality under these circumstances, they have been excited to germi-
nation when at last exposed to the requisite conditions. Thus Pro-
fessor Lindley states as a fact, that he has raised three raspberry-plants
from seeds taken from the stomach of a man, whose skeleton was found
thirty feet below the surface of the earth, at the bottom of a barrow
which was opened near Dorchester ; as his body had been buried
with some coins of the Emperor Hadrian, there could be no doubt
that the seeds were 1600 or I'TOO years old. Again, there are un-
doubted instances of the germination of grains of wheat, which were
inclosed in the wrappers of Egyptian mummies, perhaps twice that
number of years ago ; the wheat being different in some of its charac-
ters from that now growing in the country.

48. These facts make it evident, that there is really no limit to the
duration of this condition ; and that when a seed has been thus pre-
served for ten years, it may be for a hundred, a thousand, or ten
thousand, — provided no change of circumstances either exposes it to
decay, or calls its vital properties into activity. Hence in cases where
seeds have been buried deep in the earth, not by human agency, but
by some geological change, it is impossible to say how long anteriorly
to the creation of man they may have been produced and buried, —
as in the following very curious instance. Some well-diggers in a
town on the Penobscot river, in the State of Maine (New England),
about forty miles from the sea, came at the depth of about twenty feet
upon a stratum of sand, which strongly excited curiosity and interest,
from the circumstance that no similar sand was to be found anywhere
in the neighbourhood, and that none like it was nearer than the sea-
beach. As it was drawn up from the well, it was placed in a pile by
itself; an unwillingness having been felt to mix it with the stones and
gravel which were also drawn up. But when the work was about to
be finished, and the pile of stones and gravel to be removed, it was
necessary also to remove the sand-heap. This, therefore, was scat-
tered about the spot on which it had been formed, and was for some
time scarcely remembered. In a year or two, however, it was per-
ceived that a large number of small trees had sprung from the ground
over which the heap of sand had been strewn. These trees became
in their turn objects of strong interest, and care was taken that no
injury should come to them. At length it was ascertained that they
were Beach-Plum trees ; and they actually bore the Beach-Plum,
which had never before been seen, except immediately upon the sea-
shore. The trees had therefore sprung from seeds, which were in the
stratum of sea-sand, that had been pierced by the well-diggers. By
what convulsion they had been thrown there, or how long they had

SCIENCE OF PHYSIOLOGY. 45

quietly slept beneath the surface, cannot possibly be determined with
exactness ; but the enormous length of time that must have elapsed,
since the stratum in which the seeds were buried formed part of the
sea-shore, is evident from the accumulation of no less than twenty
feet of vegetable mould upon it.

49. Numerous instances will be related in the succeeding Chapter,
of the occurrence of a similar condition in fully-developed Plants, and
even in animals of high organization. In some of these it is a regular
part of the history of their lives, coming on periodically like sleep ;
whilst in others it is capable of being induced at any time, by a
withdrawal of some of the conditions essential to vital activity. In
regard to all of them, however, it may be observed, that the vitality
can only be retained, w^hen the organized structure itself is secluded
from such influences as would produce its decay. Thus the hard dry
tissue of the seed is but little liable to decomposition ; and all that is
usually required for the prevention of change in its structure, is seclu-
sion from the free access of air and from moisture, and a steady low
or moderate temperature. If a seed be exposed to air and moisture,
but the temperature be not high enough to occasion its germination,
it will gradually undergo decay, and will consequently lose its vitality.
The animal tissues are more liable, as already mentioned, to sponta-
neous decomposition ; and the only instances in which they can retain
their vitality for a lengthened period, without any nutritive actions,
are those in which all decomposition is prevented, either by the action
of cold, or by the complete deprivation of air or of moisture — as
when Frogs, Snakes, &c., have been preserved for years in an ice-
house, or Wheel-Animalcules have been dried upon a slip of glass.

50. The class of phenomena last brought under notice, serves to
exhibit in a very remarkable manner the dependence of all Vital
Action, upon certain other conditions, than those furnished by the
organized structure possessed of vital properties. Thus a seed does
not germinate of itself ; it requires the influence of certain external
agents, such as warmth, — air, and moisture ; and it can no more pro-
duce a plant without the operation of these, than warmth, air, and
moisture could produce it of themselves. Hence these agents supply
a set of conditions which are equally essential to vital action, with
the properties of the organized structure itself; and as they excite
those properties, or call them into activity, they are termed Vital
Stimuli. Now^ we have in this fact a complete analogy with the
phenomena which we may elsewhere notice. Thus, as already
pointed out, the property of mutual attractiveness between masses of
matter is only manifested, when more than one mass is present ; and
unless that condition be supplied, the property remains dormant. Or,
again, the attractive property of a magnet is only manifested, when a
piece of iron is brought into its proximity. We find still closer ana-
logies in the phenomena of Chemistry ; thus there are many chemical
operations, which require a certain amount of heat as a necessary
condition ; and the heat may be justly said to be the stimulus to the

46 NATURE AND OBJECTS OF THE

chanpje. We find, indeed, that the amount of heat is even capable of
subversing the relative affinities of two bodies for a third ; and that
thus two changes of an opposite character may be induced by the
simple regulation of temperature. For example, at a white heat, the
affinity of iron for oxygen is so much stronger than that of potassium,
that, by placing iron in contact with potassa, the latter is decomposed,
and the result is oxide of iron and potassium. At ordinary tempera-
tures, on the other hand, the affinity of potassium for oxygen is much
the stronger of the two ; and if potassium and oxide of iron be then
brought to act upon each other, the oxygen quits the latter, and
restores the former to the condition of potassa. Hence we may
justly say, that a particular temperature is the stimulus to each of
these actions. In the same manner, the influence of light is con-
cerned in producing a large number of chemical changes, including
all those which are concerned in the formation of Photographic pictures
of various kinds ; the materials concerned in these changes remain
dormant or inactive, so long as they are not subjected to its influence ;
but when it is allow^ed to operate upon them, it gives occasion to
acts of decomposition and new combination, to which acts it may be
properly said to be the stimulus.

51. Hence the dependence of Vital actions upon certain external
stimuli, as well as upon the properties of the organism w^hich manifest
them, is no greater than the dependence of any of the phenomena,
exhibited by an inorganic substance, upon some other agency external
to itself. In fact, no change whatever can he said to be truly sponta-
neous; that is, no property can manifest itself, unless it be called into
action by some stimulus fitted to excite it. Thus when spontaneous
decomposition (as it is commonly termed) occurs in an organized or
inorganic substance, it is due to the forces generated by the mutual
attraction between certain elements of the substance, and the oxygen
of the atmosphere ; and this attraction is sufficient to overcome the
attraction, which tends to hold together the particles in their original
state. If the air be totally excluded, decay will not take place ;*
because no new force comes into operation, to cause a separation of
the components from their original modes of union. The influence
of the Vital Stimuli, — that is, the conditions in regard to Heat, Light,
&c., which are essential to Vital activity, — will be fully explained in
the next Chapter ; and at present it will be sufficient to remark, that
the degree in which they are supplied possesses a well-marked
influence upon the amount of activity and energy manifested in the
actions of the organized structure ; that there is a limitation in the
case of each of them, as to the degree in which it can operate bene-
ficially, the limitation being usually narrower and more precise, accord-
ing to the elevation of the being in the scale ; that an excessive supply

* On this principle, meats, vegetables, and even liquid sonps, are now largely pre-
served, for the use of persons undertaking long voyages; by enclosing them in tia
cases, carefully soldered up. There is no limit to the time, during which decompo-
sition may thus be prevented.

SCIENCE OF PHYSIOLOGY. 47

may be destructive to the vital properties of the structure, by over-
stimulating it and thus causing it to live too fast, or by more directly
producing some physical or chemical change in its condition ; and that
a deficiency will keep down or suspend all vital activity, leaving the
structure to the unrestrained operation of those agents which are
always tending to its disintegration, and consequently occasioning a
speedy loss of the vital properties, — save in those cases in which they
may be preserved in a dormant condition, and which are exceptions
to the general rule, that the death or departure of the vital properties
follows closely upon the cessation of vital actions.

52. Our fundamental idea of Life^ then, is that of a state of con-
stant change or action ; this change being manifested in at least two
sets of operations ; — the continual withdrawal of certain elements from
the inorganic world ; — and the incorporation of these with the peculiar
structures termed organized, or the production from them of the germs
that are hereafter to accomplish this. As the conditions of this con-
tinual change, we recognize the necessity of an organized structure
on the one hand, or of a germ which is capable of becoming so;
whilst we also perceive the necessity of a supply of certain kinds of
matter from the inorganic world, capable of being combined into the
materials of that structure, which may be designated as the alimentary
substances; and, further, we see that the organism can exert no influ-
ence upon these, except with the assistance of certain other agencies,
such as light, heat, &c., which are termed vital stimuli. This ex-
pression includes all the essential phenomena of vegetative or organic
life ; whether as witnessed in the lowest or highest members of the
Vegetable kingdom ; or as displayed in a large proportion of the
structures composing the Animal fabric.

53. But just as we find among Inorganic bodies, that various
kinds are to be distinguished by their different properties, whilst all
agree in the general or essential properties of matter, so do we find
that living organized substances are distinguished by a variety of pro-
perties inherent in themselves, whilst they all agree in the foregoing
general or essential characters. In many instances, the difference of
their properties is as obviously coincident with differences in their
structure and composition, as it usually is among the bodies of the
Mineral world : thus we always find the property of Contractility on
the application of a stimulus, restricted to a certain form of organized
tissue, the Muscular ; and we find that the property by which that
stimulus is capable of being generated and conveyed to a distance, is
restricted to another kind of tissue, the Nervous. In a great number
of cases, however, very obvious differences in properties manifest
themselves, when no perceptible variations exist, either in structure or
composition ; thus it would be impossible to distinguish the germ-cell
of a Zoophyte from that of Man, by any difference in its aspect or
composition ; yet neither can be developed into any other form than
that of the parent species, and they must be regarded, therefore, as
essentially different in properties. In the same manner we shall find

48 CONNECTION BETWEEN VITALITY AND ORGANIZATION.

that, in the same organized fabric, there are very great varieties in the
actions of its component cells, which indicate a similar variety in
their properties ; and yet they are to all appearance identical. But
there can be no reasonable doubt, that differences really exist in such
cases ; though our means of observation are not such as to enable us
to take cognizance of these, by the direct impressions they make upon
our senses. Analogous instances are not wanting in the Mineral
world ; for the Chemist is familiar with a class of compounds de-
signated isomorphous, in w^hich, with perfect similarity in external
form and physical properties, there is a difference, more or less com-
plete, in chemical composition.

54. Whatever may be the peculiar vital properties possessed by an
organized tissue, we find that they are always dependent upon the
maintenance of its characteristic structure and composition, by the
nutritive operations of which we have spoken ; and that they thus
form a part, as it were, of the more general phenomena of its Life.
They manifest themselves with the first complete development of the
tissue ; they are retained and exhibited so long as active nutritive
changes are taking place in it; their manifestation is weakened or
suspended if the nutritive operations be feebly exerted; and they de-
part altogether, whenever, by the cessation of those actions, and the
uncompensated influence of ordinary Chemical forces, the structure
begins to lose that normal composition and arrangement of parts,
which constitutes its state of organization. Hence we may regard
these peculiar properties as conformable, in all the essential condi-
tions of their existence, with those more general properties, which
have been previously dwelt upon as characterizing a living organized
structure.

3. Connection between Vitality and Organization.

55. The idea that new properties may be called forth or developed
by a new combination of elements, and by a new arrangement of par-
ticles,— and that, consequently, the class of properties included under
the general term vital is dependent upon the peculiar state of matter
which is designated as organized, — is so perfectly conformable to
what is seen elsewhere, and is so fully sufficient to explain all ob-
served phenomena, that it would scarcely seem necessary to use any
further argument in support of it. But the notion has been enter-
tained, that Vitality is a something superadded to matter, and that it
is absurd to suppose that the phenomena of Life can be produced by
any combinations of matter ; and this indeed so generally prevails,
that it seems desirable to carry our investigations with regard to the
causes of Vital phenomena a little further.

56. We have seen that the properties of any kind of matter, even
those with which we are most familiar, require certain conditions for
their manifestation. Even the properties of which we take most
direct cognizance by our senses, do not manifest themselves to us,

CONNECTION BETWEEN VITALITY AND ORGANIZATION. 49

until they have made a change in the condition of our own organs. And
in regard to those, which require a stimulus of some kind to call them
into action, our acquaintance with them entirely depends upon whether
the conditions of their action have been afforded. Thus, to go back
to a former illustration, supposing a new chemical element to be dis-
covered, we could not know its properties in regard to heat, electri-
city, or magnetism, the mode of its combination with other elements,
the nature and properties of the compounds produced, their reactions
with other compounds, &c. &c., until we have tried a complete series
of experiments upon it, — that is, until we have placed it in all the
circumstances or conditions requisite to manifest the properties, with
which we seek to become acquainted, or whose absence we seek to
determine if they do not exist. Now we might have made all the
experiments we could devise upon such a body ; and yet we might
have failed in detecting some remarkable and distinguishing property
inherent in it, simply because w^e had not placed it in the requisite
circumstances for the manifestation of this peculiarity. Further, even
in the elements or compounds with w^hich we are best acquainted, it
is very possible that properties exist, of which we as yet know no-
thing, simply because they have not yet been called into action by
the requisite combination of conditions. For example, no one would
have thought it possible, a few years since, that water could be frozen
in a red-hot metallic vessel ; and yet this is now know^n to be effected
with ease and certainty, in the proper combination of conditions.

57. Again, it is by no means a sufficient definition of one of these
elements, — Oxygen, for example, — to enumerate its properties in its
simple or uncombined state ; these are the properties of oxygen gas ;
but a complete enumeration of the properties of oxygen itself w^ould
include a reference to those of every compound substance into which
it enters, as well as to the conditions under which they manifest them-
selves. We are accustomed to think of the properties of these com-
pounds, as if they were something altogether distinct from those of
the elements of which they are composed ; thus in considering the
properties of water, we commonly lose sight of the fact, that it is
formed by the union of oxygen and hydrogen, and that we must re-
gard these elements as possessing, in a dormant state, the capability
of manifesting such properties, when they are brought together under
certain conditions. Yet we cannot reason upon the ordinary opera-
tions of Chemistry, without coming to the conclusion?^ that the very
act of combination calls forth or develops properties, which were
pre-existent in the components, and which became manifest as soon
as these were placed in the circumstances required to display them.

58. It must not be forgotten, that the properties of a compound
substance are, in general at least, altogether different from those which
present themselves in either of its components ; so that we could not
in the least degree judge of the former from the latter, or of the latter
from the former. What more different, for example, from the physi-
cal and chemical properties of Water, from those of either the Oxygen

4

50 CONNECTION BETWEEN VITALITY AND ORGANIZATION.

or the Hydrogen that enter into its composition ? Or what more dif-
ferent than the properties of a neutral salt, from those of the acid and
alkali by whose union it is produced ? We are continually witness-
ing, then, the complete change effected in the sensible properties of
bodies, by acts of combination or separation ; these acts calling forth
or developing properties that were previously dormant, and reducing
to the dormant condition those which were previously sensible. That
this is the true way of accounting for the phenomena would appear
from the fact, that in all cases the converse change brings back the
original properties ; thus the oxygen and hydrogen resulting from the
decomposition of water, have all the properties of oxygen and hy-
drogen that are being combined into water. Their properties, then,
have undergone no real change ; the ostensible change being due to
the development of some of the properties of the elements, and the
reduction of others to the dormant state, by the very alteration of
their conditions. — Even a change in the condition of a single body,
without any combination, may cause new properties to be manifested
by it, and old ones to become dormant. Thus the particles of water
have so strong an attraction for each other, at a low temperature, as
to become aggregated in a crystaline form, and to produce a dense
solid mass ; at somewhat a higher temperature, their mutual attraction
is so slight, that a very small amount of mechanical force is sufficient
to separate them, and they move upon each other with the utmost
freedom ; whilst at a still higher temperature, they manifest a power
of mutual repulsion, which increases with the greatest rapidity with
every augmentation of temperature. Yet when the temperature of
the substance is lowered to its former standards, we observe that it
first returns to the liquid, and then to the solid form ; and that, in
those states, it manifests all the properties which before characterized
it,

59. Again, not merely the physical, but the chemical properties of
bodies may be affected by a change in their mechanical condition.
Thus, it is well known that oxygen and iron, at ordinary tempera-
tures, have a mutual affinity, which is only sufficient to produce a
slow combination between them ; whilst at high temperatures, that
affinity is such as to cause their rapid and energetic union. Now if
iron, in a state of very minute division, — such as it possesses when
set free from the state of oxide by means of hydrogen, at the lowest
possible temperature, — be brought into contact with oxygen or even
with atmospheric air, at ordinary temperatures, it immediately be-
comes red-hot, and is converted into an oxide. The minuteness of
the division, predisposing to chemical union, appears to be the occa-
sion of our power of causing many substances to combine, when one
or both are in the nascent state (that is, when just set free from some
other combination), which could not be made to unite in any more
direct manner ; thus, when a quantity of any preparation of Arsenic,
however minute, is dissolved in fluid in which hydrogen is being
generated, the hydrogen will detach the m^etal from its previous com-

I

CONNECTION BETWEEN VITALITY AND ORGANIZATION. 51

bination, and will pass forth in union with it, as arseniuretted hydro-
gen,— a compound which cannot be formed by the direct union of
the elements. In like manner, in that mechanical mixture of three
finely-divided substances, which we call Gunpowder, the rapidity
with which combustion is propagated through the largest collection
of it, is entirely dependent upon the minute subdivision of its com-
ponents, and the very close approximation of their particles. Hence
it may be very correctly said, that the true chemical properties of the
substances are not manifested, except when they are in a state of very
minute division ; and that these are in fact obscured, by the aggrega-
tion of the particles into masses.

60. Thus, then, we are at no loss to discover examples, in the
Inorganic world, of an interchange of the sensible properties, both
Chemical and Physical, of the bodies composing it, by a change in
the conditions in which they are placed. And it may be stated as a
general fact, that we never witness the manifestation of new proper-
ties in a substance, unless it has undergone some change in its own
condition, of which altered state these properties are the necessary
attendants. We have no right, therefore, to speak of any property as
distinct horn the matter which exhibits it; or as capable of being
superadded to it, or subtracted from it. On the other hand we are led
to the conception oi properties as either dormant or latent^ on the one
hand; or as active or sensible on the other; the difference being
entirely due to the condition of the substance. Thus, oxygen and
hydrogen have a latent or dormant affinity for each other ; this does
not manifest itself in either of them, so long as they are separate; nor
does it manifest itself at ordinary temperatures, when they are min-
gled together. But if through such a mixture we transmit an electric
spark, or if we raise the temperature of the smallest part of it by the
contact of a heated body, or if we simply introduce into it a portion
of platinum in a state of minute division, the requisite stimulus or
excitation is given to these affinities, and chemical union of the two
substances is the result.

61. Now if we apply these views to the phenomena of Life and
Organization, we see that they enable us to regard these phenomena
as analogous in character to those of the Inorganic world, though not
identical with them ; and they lead to a simplification of our ideas of
them, which more clearly marks out the path to be pursued in their
investigation. We find that the essential materials of Animal and
Vegetable structures are the four elements. Oxygen, Hydrogen, Car-
bon, and Nitrogen ; these are distinguished by the extraordinary
number and variety of the combinations into which they will enter, —
so much so, indeed, as to constitute, in this respect, a group quite
distinct from all the other elementary substances. Now we are per-
fectly justified by what we elsewhere see, in attributing to these ele-
ments the property or dormant capability of exhibiting vital actions
(in addition to the ordinary chemical ones with which we are fami-
liar), so soon as they are placed in the requisite conditions; in other

52 CONNECTION BETWEEN VITALITY AND ORGANISATION.

words, as soon as they are made a part of the living system by the
process of Organization. It is only the peculiarity of the conditions
required to manifest this capability, which prevents us from recogniz-
ing it as an ordinary property of matter, or at least of those forms
of it, which we know by experience to be capable of entering into
organized structures.

62. Thus we perceive, that Vital properties are called forth or de-
veloped in the substance of the germ, whilst this substance is being
organized by the agency of its parent; these vital properties are such
as to give it the means of assimilating and organizing the materials
supplied by the inorganic world, and whilst thus making them a part
of its own structure, to cause them to manifest their vital properties ;
and these are exercised in their turn, in making further additions to
the growing structure, and in the formation of the reproductive germ.
In this germ we cannot perceive a single trace of the future being ;
the various organs and structures of which are evolved by a process
of subsequent development. And it is probable that, in the complete
organism, not a single particle remains of those which originally con-
stituted its germ. Now it seems absurd to suppose that in a single
cell- germ, a molecule almost invisible with a high magnifying power,
a force is concentrated, which is afterwards to be diffused through the
whole structure of a vast tree; or through the ever-changing fabric of
a complex animal ; and which is not only to animate the individual
organism, but is to occasion the production of thousands or tens of
thousands of germs, each possessing a similar force, and capable of
imparting it to their successors. On the other hand, if we suppose
that the germ calls forth, or excites, the dormant properties of the
combining elements (like the spongy platinum, or the electric spark,
in a mixture of oxygen and hydrogen), — that it thus originates, first
a chemical combination, and then a peculiar structural arrangement,
— that in consequence of this new combination and arrangement, the
elements then manifest peculiar properties in place of their old ones,
which last as long as they exist in that condition, — that, when their
union in the organized fabric is dissolved, they lose these newly-
manifested properties, return to their original form, and manifest
precisely the same properties as before they were combined, — and
that they are capable of being thus operated on, time after time, their
properties not being added to, or lost, but those which were latent
being developed, and those which were at first sensible becoming
latent, — we get rid of every difficulty, at the same time that we reason
in accordance with the fundamental principles of Logic and Philoso-
phy, which forbid us to assume any agency that is not requisite to
explain the phenomena.

63. The elements. Oxygen, Hydrogen, Carbon and Nitrogen, in
a certain state of combination and arrangement, form the substance
which we term Muscular fibre ; and they then manifest certain pecu-
liar properties, which we designate as vital. On the other hand,
those same elements exist in nearly the same proportions, but in a

CONNECTION BETWEEN VITALITY AND ORGANIZATION. 53

different state of combination and arrangement, in the substance
which we term Cyanate of Ammonia ; and they then exhibit a differ-
ent set of properties, which we call Physical and Chemical. Now
we have just as much right to say, that the contractility of muscular
fibre results from the peculiar combination and arrangement of the
elementary particles in its substance, as we have to say that the solidi-
ty, translucency, hardness, and other qualities of the salt (all of which
are opposed to the vital properties, and cannot co-exist with them),
are necessarily connected with its peculiar mode of combination and
crystaline aggregation. If we were acquainted with these elements
only as they exist in organic compounds, their transposition into a
crystaline salt would be almost as marvelous to us, as the opposite
change is now.

64. The general history of the Phenomena of Life is fully conform-
able with the view, that the Vital properties of a tissue are dependent
upon that state of combination and arrangement which is termed
Organization. As long as each tissue retains its normal or regular
constitution, renovated by the actions of absorption and deposition
through which that constitution is preserved, and surrounded by those
other conditions which a living system alone can afford, so long, we
have reason to believe, it will retain its vital properties, — and no
longer. And just as we have no evidence of the existence of vital
properties in any other form of matter than that which we call organ-
ized, so have we no reason to believe that organized matter can re-
tain its regular constitution, and be subjected to its appropriate
stimuli, without exhibiting vital actions. The advance of pathological
science renders it every day more probable (indeed the probability
may now be said to amount to almost positive certainty), that de-
rangement in function, — in other words, an imperfect or irregular
action, — always results, either from some change of structure or com-
position in the tissue itself, or from some corresponding change in the
stimuli by which the properties of the organ are called into action.
Thus, when a Muscle has been long disused, it can scarcely be ex-
cited to contraction by the usual stimulus, or may even be altogether
powerless; and minute examination of its structure shows it to have
undergone a change, which is obvious to the microscope, though it
may not be perceptible to the unaided eye, and which results from
imperfect nutrition. Or, again, convulsive or irregular actions of the
Nervous system may be produced, not by any change in its own com-
position, but by the presence of various stimulating substances in the
blood, although their amount be so small that they can scarcely be
recognized.

65. As there is a constant tendency, in the Animal tissues more
especially, to spontaneous decay, so must the maintenance of the vital
properties depend upon their continual regeneration by the nutritive
operations. Hence we have no difficulty in accounting for the Death
of the whole system, on the cessation or serious disturbance of any one
important function ; for any such check or change must suspend or

54 CONNECTION BETWEEN VITALITY AND ORGANIZATION.

disorder the nutrient processes, in such a degree that they can no
longer maintain the normal constitution of the several tissues. But
as there is a great variety in the rapidity of the decomposition of the
tissues, when the act of nutrition is suspended, so do we witness a
corresponding variety in the duration of their vital properties, after
that permanent severance of the chain of functions, which is distin-
guished as somatic death, — i. e., the death of the body as a whole.
It is by the Circulation of the Blood, that the connection of the dif-
ferent functions is essentially maintained ; that fluid being not only
the material for the nutrition of the tissues, but in many cases serving
also as the stimulus to their activity. Hence with the permanent
cessation of the Circulation, 5oma/ic death must be regarded as taking
place.

66. Yet after this, we observe that vitality lingers in the tissues;
and that it departs from them only as they lose their proper composi-
tion. Thus we find that, although the Nervous centres cannot originate
the stimulus necessary to produce Muscular contraction, after the Cir-
culation has ceased, — yet the Nervous^6re5 can convey such a stimu-
lus, long after somatic death ; so that contractions may be excited in
muscles by the application of galvanism, or of mechanical or chemical
stimulants, to the trunks that supply them. The molecular death of the
Nervous tissue, therefore, has not yet taken place. After a time, how-
ever, this power is lost ; the tissue no longer exhibits its distinguishing
vital properties ; and incipient decomposition and change of structure
manifest themselves. Yet for some time after this, the Muscular
tissue, especially in a cold-blooded animal, continues to possess its
peculiar contractility ; for contractions may be excited in it, by stimuli
directly applied to itself, long after the nerves have ceased to convey
their influence. Sometimes, indeed, the contractility of muscle endures,
until changes in its structure and composition become evident to the
senses; thus the heart of a Sturgeon, removed from the body, and hung
up to dry, has been known to continue alternately contracting and
dilating, until the movement produced a crackling noise, in conse-
quence of the dryness of the texture. Again, there is evidence, that
various processes of nutrition and secretion may go on, for some time
after somatic death, and even after the removal of the organs from the
body, provided a sufficient quantity of blood remains in them ; and the
blood itself retains its vitality, so as not to coagulate, whilst contained
in the vessels of tissues still living.

67. Hence it is, that parts which have been completely separated
from the body may often be reunited with it, if they were previously
in a healthy state, and too much time has not elapsed ; thus, there
are many cases on record, in which fingers, toes, noses, or ears, that
have been accidentally chopped off, have been made to adhere and
grow as before, by bringing the cut surfaces into contact, even some
hours after their severance. It is evident, then, that the parts so
severed cannot have lost their vitality; since no treatment could pro-
duce union between a dead mass and a living body. And we are

CONNECTION BETWEEN VITALITY AND ORGANIZATION. 55

fully justified in assuming that, in cases where attempts at such re-
union have not been successful, the death of the separated part has
resulted from the too-prolonged interruption of its regular nutritive
operations, whereby chemical and physical changes have taken place
in it, and destroyed the peculiar structure and composition of its
several parts. The ordinary phenomena of Death, therefore, as well
as those of Life, bear out the views which have been here advanced.

68. But it has been maintained by those who consider Vitality as
something superadded to an Organized Structure, essentially independ-
ent of it, and capable of being subtracted from it, that Death fre-
quently takes place under circumstances, which leave the organism
as it was ; so that " the dead body may have all the organization it
ever had whilst alive." For such an assumption, there is not the
least foundsstion. In nearly all cases in which death takes place as
a result of disease, the connection between changes of structure and
composition, either in the tissues or in the blood, and such a loss of
the vital properties of some part or organ as is sufficient to bring the
Circulation to a stand, is so palpable as to require no proof; and in
by far the greater majority of cases in which it is not at once obvious,
a more careful scrutiny will reveal it. It must be confessed on both
sides, that our means of investigation, and our knowledge of the
normal structure and composition of the tissues and the blood, are
not yet sufficient to enable us to detect minute shades of alteration,
nor to assert what extent of change is inconsistent with the continu-
ance of life. And as no one has yet shown, by the careful and exact
microscopical and chemical examination of the solids and fluids of a
dead body, that it has all the organization it had whilst alive, the
assertion above quoted is totally unwarranted by experience, and is
contradicted by all our positive knowledge of the matter. (See §
187.)

69. But it has been urged, that Death may result from the sudden
operation of some agency of an immaterial character, which leaves
no trace behind it, — such as a powerful electric shock, or a violent
mental emotion. Here, too, the argument entirely fails. It is impos-
sible that a powerful electric shock could be transmitted through a
mass like the animal body, composed of elements in such a loose
state of combination that they are always undergoing decomposition,
without producing important chemical changes in it ; and its imper-
fect conducting power renders it equally liable to physical disturb-
ances. As a matter of fact it has been noticed, that the bodies of
animals killed by electricity pass into decomposition with unusual
rapidity ; showing that the ordinary chemical affinities of their com-
ponents have received a powerful stimulus; and it has also been
ascertained, that when Eggs in process of development have had
their vitality destroyed by an Electric shock, the minute vessels of
the vascular area (Chap. XI.) have been ruptured. — Nor is it more
difficult to explain the immediate cause of death, as a result of Men-
tal emotion. In some cases, an obvious physical change has been

56 CONNECTION BETWEEN VITALITY AND ORGANIZATION.

produced by the too violent action of the heart, the movements of
which are stimulated by the emotion ; thus, even in a healthy person,
rupture of the heart or aorta has been known to take place, an occur-
rence to which those affected by previous disease of that organ are
much more liable. Where there is any disorder in the heart's action,
resulting from thickened valves, narrowed orifices, &c., the physical
influence of mental emotion can be easily accounted for. But it
must be admitted that cases have occurred, in which no such explana-
tion can be offered ; sudden death having taken place without any
perceptible structural cause. We are not obliged, however, to have
recourse to any hypothesis for an explanation of even these cases,
which is not borne out by ample analogy. For it is well known that
mental emotions exert a powerful influence over the composition of
the fluids of the body, and are capable of instantaneously altering
these. Thus in many human beings, and still more in the lower
animals, alarm or agitation will occasion the immediate disengage-
ment of powerfully odorous secretions, which must have resulted
from new combinations suddenly formed. And there can be no
doubt that a fit of passion may immediately occasion such a change
in the milk of a nurse, as renders it a rank poison to the infant.
There is no reason to doubt, therefore, that the blood itself may
undergo changes of analogous character from the same cause ; and
that it may become a violent poison to the individual himself, instead
of being the source of wholesome nutriment, or the stimulus to vital
activity.

70. To conclude, then ; — we only know of Vital action^ as exhi-
bited by an Organized structure, under the influence of certain stimuli;
and we only know of Vitality^ or the state or endowment of the being
that exhibits that action, as conjoined with that particular aggregation
and composition which we term Organization. The real cause of
that endowment must be traced to the properties of the original ele-
ments of the structure exhibiting it, and to the conditions under
which they came into action. We have thus two objects for con-
sideration, in regard to the process of organization and the develop-
ment of the vital properties ; namely, the original component elements,
and the organizing germ which is the means of bringing them into
combination. The former are permanent in their character, for what-
ever be the nature of the changes they are made to undergo, in the
various acts of combination, they manifest their original properties
when restored to their pristine state, and can thus be successfully
made to form part of innumerable compounds, organic or inorganic.
On the other hand, the properties of the germ are but transitory ; its
own existence, as well as the duration of the entire organism to which
it gives rise, is limited ; and the whole Organized Creation would
speedily come to an end, and would be resolved into its pristine
elements, if a provision had not been made in the reproductive pro-
cess, for antagonizing the continual decay of living beings by a con-
tinual succession.

CONNECTION BETWEEN VITALITY AND ORGANIZATION. 57

71. For the existence of those dormant properties in the elements
commonly termed inorganic, which enable them to become component
parts of organized structures and then to perform vital actions, we can
assign no other cause than the Will of the Creator. The constancy
of the actions which result from them, when the conditions are the
same, — that is, their conformity to a fixed plan, or (in the language
commonly employed) their subordination to laws^ — indicates the con-
stancy and unchangeableness of the Divine Will, as well as the Infinity
of that Wisdom, by which the plan was at first arranged with such
perfection, as to require no departure from it, in order to produce the
most complete harmony in its results.

72. So also, if we endeavour to assign a cause for the existence of
a cell-germ, we are led at first to fix upon the vital operations of the
parerital organism by which it was produced.; and for these we can
assign no other cause than the peculiar endowments of 27^ components,
brought into activity by the cell-germ that originated it. Thus we
are obliged to go backw^ards in idea from one generation to another ;
and when at last brought to a stand by the origin of the race, we are
obliged to rest in the Divine Will as the source of those wonderful
properties, by which the first germ developed the first organism of the
race from materials previously unorganized, this organism producing a
second germ, the second germ a second organism, and so on without
limit, by the uniform repetition of the same processes. Yet we are
not to suppose that the continuation of the race is really in any way
less dependent upon the Will of the Creator, than the origin of it.
For whilst Science leads us to discard the idea that the Deity is con-
tinually interfering^ to change the working of the system He has made,
— since it everywhere presents us with the idea of uniformity in the
plan, and of constancy in the execution of it, — it equally discourages
the notion entertained by some, that the creation of matter, endowed
with certain properties, and therefore subject to certain actions, was
i\i& final act of the Deity, as far as the present system of things is con-
cerned, instead of being the mere commencement of His operations.
If it be admitted, that matter owes its origin and properties to the
Deity, or, in other words, that its first existence vj^ls but an expression
of the Divine Will, what is its continued existence, but a continued
operation of that same Will ? To suppose that it could continue to
exist, and to perform its various actions, hy itself, is at once to assume
the property of self-existence as belonging to matter, and thus to do
away with the necessity of a Creator altogether ; — a conclusion to
which it may be safely aflSrmed that no ordinarily-constituted Man
can arrive, who reasons upon the indications of Mind in the pheno-
mena of Nature, in the same way as he does in regard to the creations
of Human Art.

58 VITAL STIMULI.

CHAPTER II.

OF THE VITAL STIMULI.

73. It has been shown in the preceding Chapter, that the most
general conditions of Vital phenomena are two-fold ; — one set being
supplied by the organized structure, which is endowed (in virtue of
its organization) with certain peculiar properties, but which is inert so
long as it is altogether secluded from the influence of external agents ;
— and the other being furnished by external agents of various descrip-
tions, some of which supply the materials from which the organized
structure is built up, whilst others serve to stimulate or excite the
process of organization, or call forth the peculiar properties of the
organized structure. Thus in the case of the germinating seed, the
embryo within, possessed of a peculiar organization, and capable of
development into a living fabric of complex structure, remains in a
dormant state, until it is aroused to activity by the influence of warmth,
air, and moisture. Here, then, we have the distinction between the
organism and the external agents most palpably exhibited. No vital
activity can manifest itself without the concurrence of both; and the
germ could no more produce a plant without the materials supplied to
it by the external world, and the stimuli which excite it to the action
of appropriating these, than the latter could develop themselves into
a plant, without the formative agency of the germ.

74. In this dependence of Vital action upon the concurrence of
several conditions, we only see that which is true, under a simpler
form, of Chemical action ; and here, too, we trace the distinct agency
of the materials employed, and the stimuli which excite their mutual
aflSnities, and thus bring about their union. The materials of Chemi-
cal Action are the substances (either elementary or composite), which
are ready to enter into new combinations with each other ; and that
readiness or Affinity is one of their distinguishing properties. Thus
the mutual affinities of oxygen and hydrogen, or of an acid and an
alkali, are characteristic properties of these substances respectively.
Sometimes this affinity is strong enough to cause union between the
substances under any ordinary circumstances. But in many other
cases, a stimulus of some kind is necessary to bring these aflinities to
bear (so to speak) upon one another. Now the stimuli to Chemical
action belong to the class of agents commonly termed imponderable^ —
namely. Light, Heat, and Electricity; and the union between two
substances, which were previously altogether dormant in regard to
each other, although in close contact, may be frequently caused to take
place, wath various manifestations of energy, by the momentary influ-
ence of one of these agents. Thus, when chlorine and hydrogen are

VITAL STIMULI. 59

mingled together in a bottle, and this is placed in darkness, they may
be kept for any length of time without change ; but if they are exposed
to diffused daylight, they slowly Unite ; and if they be subjected to
the direct rays of the sun, instantaneous explosion takes place, with
production of hydrochloric acid. Here, then, the agency of Light
brings the previously-dormant affinities of these two bodies into a state
of activity in regard to each other. The same effect may be produced
by Heat ; for a union of the two gases, with a violent explosion, takes
place when any incandescent substance is introduced into the mixture.
And a like result is produced hy Electricity ; hydrochloric acid being
generated under the same circumstances, by the influence of the
electric spark. "*

75. In like manner it is requisite to distinguish, among the external
agents that concur with the organic germ to produce an organized
structure, between those which furnish the materials of that structure,
or which enter into chemical union with its elements, and those which
act as stimuli to its actions ; and we find that this distinction coincides,
as in the former case, with the division between the ponderable or
material, and the imponderable agents. Under the former group are
included the various elements, which are capable of being appro-
priated by the organism as the materials of its own structure, and
which are possessed of peculiar propAies that are then developed ;
in other words, the various articles of food. The oxygen of the
atmosphere, whose union with certain elements of the organism, in
the process of Respiration, is also an agent essential to its functional
activity, — belongs to the same division. The general dependence of
the living organized body upon food and oxygen, has been, however,
already noticed ; and it will be preferable to defer the detailed con-
sideration of the mode and conditions under which they act upon it,
until the history of the Nutritive operations is more fully entered upon.
This will be the fitting opportunity, however, for the examination of
the general influence of the Imponderable agents, and of some others
which cannot be so well treated of elsewhere.

76. In regard to all these Vital Stimuli it may be observed, that
the dependence of Vital Action upon their constaiit influence is greater
in proportion to the high organization of their structure, and vice versa;
so that beings of simple organization are capable of enduring a depri-
vation of these stimuli, which would be fatal to those higher in the
scale. This will be partly understood, when it is borne in mind that
the higher the development of the living being, the more complete is
the distribution of its different actions amongst separate organs, — the
more close, therefore, is their mutual dependence, — and the more
readily, in consequence, are they all brought to a close by the inter-

* Although the conditions of this union appear linDited to the mutual proximity of
the two bodies, and to the influence of one of these three stimuli, yet it may be asserted
that they are probably more complex than they appear; for although a high tempera-
ture is competent to produce their union when Heat is employed alone, yet it is pro-
bable that neither Light nor Electricity would suffice to effect it, if they were Dot kepi
in the gaseous state by the large amount o{ latent heat they possess.

60 VITAL STIMULI.

ruption of any one. But there is no doubt, that the actions of even
the individual parts of the higher organisms require for their excite-
ment a greater supply of these stimuli, than the similar actions of the
corresponding parts in the lower : whilst if these stimuli be exerted
upon the lower with the intensity that is required for the higher, they
destroy the vital properties of the tissues altogether, by the excess of
their action. This distinction is most obvious in regard to the rela-
tive influence of Heat, upon warm-blooded and cold-blooded animals;
of which examples will be given hereafter.

77. It may also be observed of the influence of these, as of that of
other stimuli whose agency is less general, that it is rather relative
than absolute; being frequently dependent upon the degree of change,
rather than upon the actual measure of the amount of the stimulus.
This constitutes a marked difference between the influence of these
stimuli on mere chemical compounds, and their operation on bodies
endowed with vitality. In the former case, their action is always
uniform ; thus the same amount of heat, the same exposure to light,
the same charge of electricity, would be required to produce a given
Chemical effect, how often soever the action might be repeated. But
this is not the case with living bodies ; since an increase or diminution
in the intensity of the vital stimuli, which, if made suddenly, would be
scarcely compatible with the TOntinuance of Life, may be so brought
about, as to produce no marked change in its phenomena, — the or-
ganism possessing a certain power of adapting itself to conditions
which are habitual to it, and thus allowing great changes in these
conditions to be gradually effected, without any serious disturbance. —
Thus of two individuals of the same species, one may become torpid
at a temperature of 60°, because it has been accustomed to a tempe-
rature of 70° ; whilst another, habituated to a temperature of 60°,
would require to be cooled down to 50°, in order to induce torpidity ;
— the influence of temperature upon the vital conditions being propor-
tioned, more to the variation from the usual standard, than to the actual
elevation of that standard. Yet the first of these individuals might
be gradually habituated to live in the same temperature with the
second ; and to require the same amount of further depression to in-
duce torpidity. (See § 129.)

78. It is a very curious fact that, whilst the lower classes of living
beings are more capable than the higher of bearing the deprivation of
these Vital stimula, they are at the same time more liable to alterations
in their own structure and development, in consequence of variations
in the degree of their agency, or from other causes external to them-
selves. Thus ihe. forms of the lower tribes of Plants and Animals are
liable to be greatly affected by the conditions under which they grow ;
and these especially modify their degree of development. It seems
as if the formative power were less vigorous in the lower, than in the
higher classes ; so that the mode in which it manifests itself in the
former is more dependent upon external influences ; whilst in the
latter it either predominates over them, causing the regular actions

OF LIGHT AS A VITAL STIMULUS. 61

to be performed, or gives way altogether. — The same principle applies
to the early condition of the higher organisms ; their embryos, like
those beings of permanently low type which they resemble in degree
of development, being liable to be affected by modifying causes,
which the perfect beings of the same kind are able to resist. It is in
this way that we are to explain the influence, which the female parent
exerts upon the embryo ; the germ of which she receives from the
male, but to which she supplies the materials for its development.

1. 0/ Light ^ as a Condition of Vital Action.

79. The importance of this agent, not only to the Vegetable, but
to the Animal World, is not in general sufficiently estimated. Under
its influence alone, can the first process be accomplished, by which
inorganic matter is transformed into ^an organic compound, adapted
by its nature and properties to form part of the organized fabric. The
following is an example of the simplest phenomenon of this kind;
and it demonstrates the influence of Light the more clearly on account
of that simplicity. " If we expose some spring-water to the sunshine,
though it may have been clear and transparent at first, it presently
begins to assume a greenish tint ; and, after a while, flocks of green
matter collect on the sides of the vessel, in which it is contained. On
these flocks, whenever the sun is shining, bubbles of gas may be seen,
which, if collected, prove to be a mixture of oxygen and nitrogen,
the proportion of the two being variable. Meanwhile the green matter
rapidly grows ; its new parts as they are developed, being all day
long covered with air-bells which disappear as soon as the sun has
set. If these observations be made upon a stream of water, the cur-
rent of which runs slowly, it will be discovered that the green matter
serves as food for thousands of aquatic Insects, which make their
habitations in it. These insects are endowed with powers of rapid
locomotion, and possess a highly organized structure ; in their turn
they fall a prey to the Fishes which frequent such streams."* Such is
the general succession of nutritive actions in the Organized Creation.
The highest Animal is either directly dependent upon the Vegetable
Kingdom for the materials of its fabric, or it is furnished with these
by some other Animal, this again (it may be) by another, and so on ;
the last in the series being always necessitated to find its support in
the Vegetable kingdom, since the Animal does not possess the power
of causing the Inorganic elements to unite into even the simplest
Organic compound. This power is possessed, in a high degree by
Plants ; but it can only be exercised under the influence of Light.
We shall now examine, more in detail, the conditions of this influence,
both in the instance just quoted, and in others drawn from the actions
of the higher Vegetable organisms.

80. The " green matter of Priestley," (as it is commonly called,)

• Prof. Draper, on the Forces which produce the Organization of Plants, p. 15.

62 OF LIGHT AS A VITAL STIMULUS.

which makes its appearance when water of average purity is sub-
mitted to the action of the Sun's light, and which also pnesents itself
on the surface of walls and rocks, that are constantly kept damp, is
now known by Botanists to consist of cells in various stages of de-
velopment,— the early forms, it may be, of several different species of
Confervee. That these cells all originate from germs, and not from
any direct combination of the inorganic elements, appears not only
from general considerations, but also from the fact that, if measures
be taken to free the water entirely from any possible infusion of or-
ganic matter, and to admit into contact with it such air alone as has
undergone a similar purification, no green flocks make their appear-
ance, under the prolonged influence of the strongest sunlight. We
find, then, that the presence of a germ is one of the conditions indis-
pensable to the chemical transformation in question. It maybe asked
how it can be certainly ascertained that light and not heat is the
essential condition of this process ; seeing that the two agents are
combined in the solar beam. To this it may be replied, that a certain
moderate amount of heat is undoubtedly necessary ; but that no degree
of heat without light will be effectual in producing the change, as is
easily proved by exposing the water to warmth in a dark place.
Moreover, when a certain measure of light is afforded, variations in
the amount of heat make very little difference ; but we shall presently
see that under the same degree of heat, the amount of the change is
directly proportional to the intensity of the light. Although, there-
fore, heat furnishes an essential condition, it cannot be questioned
that light is the chief stimulus to that process, by which the germ
brings into union the elements to be employed in the development of
its own fabric.

81. The next question is, — What are these elements, and whence
are they obtained ? All water that is long exposed to the atmosphere,
absorbs from it a certain amount of its constituent gases ; but these
do not enter it in the proportions in which they are contained in the
atmosphere itself; their relative quantities, in a given measure of
water, being proportioned to the facility with which they are respect-
ively absorbed by the liquid. Thus carbonic acid is most readily
absorbable ; oxygen next, and nitrogen least so. From the expe-
riments of Prof. Draper it would appear, that notwithstanding the
very small proportion of carbonic acid contained in the atmosphere
(usually not more than l-2000th part), it forms as much as 29 per
cent, of the whole amount of air expelled from water by boiling. Of
the residue, one-third consists of oxygen, and the remaining two-
thirds of nitrogen ; so that the proportion of the oxygen to the nitro-
gen is as one to two, instead of being one io four, as in atmospheric
air. The absolute quantity of this water-gas, contained in any mea-
sure of water, is subject to variation with the temperature; the quan-
tity being diminished as the temperature rises. — Now when water
thus impregnated with carbonic acid, oxygen, and nitrogen, and con-
taining the germs of aquatic plants, is exposed to the sun's light, a

J

OF LIGHT AS A VITAL STIMULUS. 63

development of vegetable structure takes place, indicated by the green
flocculent appearance, as already mentioned. If the changes, which
are now occurring in the water, be examined, we find that the carbo-
nic acid is diminishing in amount ; and that oxygen is being evolved.
The growing mass increases in volume and weight ; and after a time
exhausts the whole carbonic acid originally contained in the water.
If then it be prevented from receiving an additional supply, the pro-
cess stops ; but as conducted naturally, there is a free exposure to
the atmosphere, through which carbonic acid is diffused ; and hence,
as fast as it is removed by decomposition, it is restored by absorption.

82. Here then are the conditions and materials ; what is the re-
sult ? As a consequent of the conjoint action of light and of a vege^
table cell-germ, with a moderate degree of heat, upon carbonic acid
and water, we find a vegetable structure produced, whose fabric con-
sists of carbon, united with the elements of water. Whether this
union is really as simple and direct, as is implied by this expression,
or whether the same proportions of oxygen, hydrogen, and carbon
are united in a different form, is not a matter of consequence to the
present inquiry ; the general fact being, that by the decomposition of
the carbonic acid, oxygen is set free, and carbon is made to unite
with the elements of water ; so as to form an organic compound,
which is appropriated by the Vegetable organism as the material for
its growth. — How far Light is also concerned in the production of
the protein-compounds (of which azote forms a part), that are pre-
pared by Plants for the use of Animals, has not been yet ascertained ;
but it is probable that these are not the less dependent upon its agency
for their formation, since they are generated under the same circum-
stances with the preceding. Indeed it may be questioned whether a
minute quantity of azote is not an essential part of the contents of every
vegetable cell, though it does not enter into the composition of the
cell-wall.

83. The process whose conditions we have thus examined, is car-
ried on in the individual cells, that compose the highest and most
complex Plants, precisely as in those which constitute the entire forms
of the lowest. Thus if a few^ garden-seeds of any kind be sown in
a flower-pot, and be caused to germinate in a dark room, it will soon
be perceived that although they can grow for a time without the influ-
ence of light, that time is limited ; the weight of their solid contents
diminishes, although their hulk may increase by the absorption of
water; their young leaves, if any should be put forth, are of a yellow
or gray-white colour, and they soon fade away and die. But if
these plants are brought out sufficiently soon into the bright sun-
light, they speedily begin to turn green, they unfold their leaves, and
evolve their different parts in a natural way ; and the proportion of
their solid contents goes on increasing from day to day. If the fabric
be then subjeeted to chemical analysis, it is found to contain oxygen,
hydrogen, carbon, and azote ; united in various proportions, so as to
form compounds that differ in the various species, though some, —

64 OF LIGHT AS A VITAL STIMULUS.

such as gum, starch, and cellulose, — are the same in all. If the
plants be made to grow in closed glass vessels, under such circum-
stances that an examination can be accurately made as to the changes
they are impressing on the atmosphere, it is discovered that they are
constantly decomposing its carbonic acid, — appropriating its carbon,
and setting free its oxygen, — so long as they are exposed to the in-
fluence of sunshine or bright daylight. They also appropriate a part
of the minute quantity of ammonia which is diffused through the
atmosphere ; extracting its nitrogen to employ it in the production of
their azotized compounds. It is capable of being demonstrated by
experiment, that these changes are confined to the green surfaces of
plants, and therefore to the leaves or leaf-like organs, the young
shoots, and the stems of herbaceous plants, or of those in which (as
in the Cactus tribe) the leaves are wanting and the enlarged succu-
lent stem supplies their place. When these surfaces cease to become
green, the decomposing action also ceases; carbon is no longer fixed,
and oxygen set free ; but, on the contrary, carbonic acid is exhaled :
this is the case when the leaves change colour, previously to their
fall, in the autumn. The compounds which are thus generated in the
green surfaces, are conveyed to the remote parts of the fabric, by the
circulation of the sap, and become the materials of their nutrition ;
and thus the green cells of the leaves have exactly the same function,
in ministering to the growth of the fabric of the largest tree, which
the green cells of the humble Conferva perform in regard to them-
selves alone.

84. It has been already mentioned, that the decay which is always
taking place in the softer vegetable structures, gives rise to a con-
tinual production of carbonic acid, even in the living plant ; this
process, which must be regarded as a true Respiration, is effected,
as in Animals, by the union of the carbon of the Plant with oxygen
derived from the atmosphere ; and it is carried on, not by the green
parts only, but also, perhaps chiefly, by the darker surfaces. Being
antagonized during the day by the converse change just described,
it can only be made sensible, by placing the plants for a time in an
atmosphere in which no carbonic acid previously existed ; and it
will then be found that, even in full daylight, a certain amount of
that gas is exhaled. The fact, however, becomes much more obvious
at night, or in darkness ; since the decomposition of the surrounding
carbonic acid by the green surfaces is then completely at a stand,
and a full effect of the respiratory process is seen. Moreover,
when a plant becomes unhealthy, from too long confinement in a
limited atmosphere, it begins to exhale more carbonic acid than it
decomposes ; and the same is the case, as just now stated, in regard
to leaves that have nearly reached the term of their lives. It does
not admit of question, however, that, under ordinary circumstances,
nearly the whole carbon of a slow-growing plant is derived from the
carbonic acid of the atmosphere ; either directly through the leaves,
or indirectly by absorption through the roots ; and that there must be

OF LIGHT AS A VITAL STIMULUS. 65

a vast surplus, therefore, of the carbonic acid decomposed, over that
which is exhaled, during the whole life of the tree, — that surplus being
in fact represented by the total amount- of carbon contained in its
tissues.

85. It is probable that the minute amount of carbonic acid at pre-
sent contained in the atmosphere, is as much as could be beneficially
supplied to Plants, under the average amount of light to which they
are subjected, over the whole globe, and throughout the year. It has
been clearly shown, that, under the influence of strong sunlight, an
atmosphere containing as much, as 7 or 8 per cent, of carbonic acid
may be not merely tolerated by Plants, but may be positively bene-
ficial to them, producing a great acceleration in their growth ; but as
soon as the light is withdrawn, it acts upon them most injuriously,
causing them speedily to become unhealthy, and altogether destroying
their vitality, if they are long subjected to it. Under more cloudless
skies than ours, however, the continual supply of a larger quantity of
carbonic acid, than our atmosphere contains, is found to be quite com-
patible with healthy vegetation ; especially in the case of Cryptoga-
mic plants, w^hich (as wdll be presently shown) require a less amount
of this stimulus than those of a higher kind. Thus in the lake Sol-
fatara in Italy, an unusual supply of carbonic acid is afforded by the
constant escape of that gas from fissures in the bed of the lake, with
a violence that gives to the water an appearance of ebullition ; and
on its surface there are numerous floating islands, which consist
almost entirely of Confervse and other simple cellular plants, growing
most luxuriantly on this rich pabulum. And it has been remarked,
that the vegetation around the springs in the valley of Gottingen,
w^hich abound in carbonic acid, is very rich and luxuriant; appearing
several weeks earlier in the spring, and continuing much later in the
autumn, than at other spots in the same district. Many circumstances
lead to the belief, that at former epochs in the Earth's history, the
atmosphere was much more highly charged with carbonic acid than
at present ; and that to this circumstance, in conjunction with a more
intense and constant influence of light and heat, we are to attribute
that extraordinary luxuriance of the vegetation of those periods, of
which we have most abundant evidence, in the vast beds of disin-
tegrated vegetable matter — Coal — that are of such value to Man, and
in the remains which have been more perfectly preserved to us, and
which indicate that not only the general forest-mass, but many of the
individual forms attained a degree of development, which cannot
now be paralleled even between the Tropics.

86. Various experiments have been recently made, with the view
of determining more precisely the conditions under w^hich Light acts,
in producing the chemical changes that have been now discussed.
These experiments for the most part agree in the very interesting re-
sult, that the amount of carbonic acid decomposed by plants subjected
to the differently coloured rays of the solar spectrum, but otherwise
placed in similar circumstances, varies with the illuminatwg power

5

66 OF LIGHT AS A VITAL STIMULUS.

of the rays, and not with their heating or their chemical power. The
method adopted by Prof. Draper, which seems altogether the most
satisfactory, consisted in exposing leaves of grass, in tubes filled with
water which had been saturated with carbonic acid (after the expul-
sion of the previously dissolved air by boiling), to the influence of
the different rays of the solar spectrum, dispersed by a prism; these
were kept motionless upon the tubes for a sufficient length of time,
to produce an active decomposition of the gas in the tubes which
were most favourably influenced by the solar beams ; and the relative
quantities of the oxygen set free were then measured. It was then
evident that the action had been almost entirely confined to two of
the tubes, one of them being placed in the red and orange part of the
spectrum, and the other in the yellow and green. The quantity of
carbonic acid decomposed by the plant in the latter of these, was to
that decomposed in the former in the ratio of nine to Jive; the quan-
tity found in the tube that had been placed in the green and blue por-
tion of the spectrum, would not amount, in the same proportion, to
one; and in the other tubes, it was either absolutely nothing, or ex-
tremely minute. Hence it is obvious that the yellow ray, verging into
orange on one side, and into green on the other, is the situation of the
greatest exciting power possessed by light on this most important func-
tion of plants ; and as this coincides with the seat of the greatest illu-
minating power of the spectrum, it can scarcely be doubted that light
is the agent here concerned ; more especially as the place of greatest
heat is in the red ray, and that of greatest chemical power is in the
hlue^ both of which rays were found to be quite inert in the experi-
ment just quoted. It must not be supposed from this experiment,
how^ever, that the yellow ray, and those immediately adjoining it, are
the only sources of this power in the Solar spectrum ; since it proves
no more than that, when the leaves were exposed to a highly car-
bonated atmosphere, they could only decompose it under the influence
of these rays. It is certain, from other experiments, that plants will
grow, in an ordinary atmosphere, under rays of different colours; and
it appears that the amount of carbon they severally fix, bears a con-
stant proportion to the illuminating powers of the respective rays.

87. Although this fixation of carbon by the decomposition of car-
bonic acid, is the most universally-dependent, of all the processes of
the Vegetable economy, upon the influence of Light, yet it is not the
only one, especially among the higher Plants, in which that agent
becomes an important condition. Of the whole quantity of moisture
imbibed by the roots, and contained in the ascending sap, a large
proportion is exhaled again by the leaves ; a small part only being
retained (together with the substances previously dissolved in the
whole) to form part of the fabric. Now upon the rapidity of this ex-
halation depends the rapidity of the absorption ; for the roots will not
continue to take up more than a very limited amount of fluid, when
it is not discharged again from the opposite extremity (so to speak)
of the stem. The loss of fluid by the leaves appears to be a simple

OF LIGHT AS A VITAL STIMULUS. 67

process of evaporation, depending in great part upon the temperature
and dryness of the surrounding air; this evaporation, however, does
not take place solely, or even chiefly, from the external surface of the
leaves, but from the walls of the passages which are channeled out in
their interior. Into this complex labyrinth, the outer air finds its way
through orifices in the cuticle, which are termed stomata ; and through
these it comes forth again, charged with a large amount of vapour
communicated to it by the extensive moist surface, with which it
comes into contact in the interior of the leaf. Now the stomata are
bounded by two or more cells, in such a manner that they can be
opened or closed by changes in the form of these ; and this alteration
is regulated by the amount of Light, to which the leaves are sub-
jected. When the stomata are opened under the influence of light,
the external air is freely admitted to the extended surface of moist
tissue within the leaf, and a rapid loss of fluid is the result; more
especially if the temperature be high, and the atmosphere in a dry
state. On the other hand, if the stomata be closed, the only loss of
fluid that can take place from the internal tissue of the leaves, is
through the cuticle ; the organization of which seems destined to
enable it to resist evaporation, so that the exhalation is almost entirely
checked. The influence of light upon this important function is
easily shown by experiment. If a plant, which is actively transpiring
and absorbing under a strong sunshine, be carried into a dark room,
both these operations are almost immediately checked, even though
the surrounding temperature be higher than that, to which the plant
was previously exposed.

88. The effect of the complete and continued withdrawal of light
from a growing plant, is to produce an etiolation or blanching of its
green surfaces; a loss of weight of the solid parts, owing to the con-
tinued disengagement of carbon from its tissues, unbalanced by the
fixation of that element from the atmosphere ; a dropsical distension
of the tissues, in consequence of the continued absorption of water,
which is not got rid of by exhalation ; a want of power to form its
peculiar secretions, or even to generate new tissues, after the mate-
rials previously stored up have been exhausted; in fine, a cessation
of all the operations most necessary to the preservation of the vitality
of the structure, of which cessation its death is the inevitable result.
A partial withdrawal of the influence of light, however, is frequently
used by the Cultivator, as a means of giving an esculent character to
certain Plants, which would be otherwise altogether uneatable ; for
in this manner their tissues are rendered more succulent and less
stringy, whilst their peculiar secretions are formed in diminished
amount, and communicate an agreeable flavour instead of an un-
wholesome rankness of taste.

89. There is one period in the life of the Flowering Plant, how-
ever, in which the influence of Light is injurious instead of beneficial ;
this is during the first part of the process of germination of seeds,
w^hich is decidedly retarded by its agency. This forms no exception,

68 OF LIGHT AS A VITAL STIMULUS.

however, to the general rule ; since the decomposition of the carbonic
acid of the atmosphere, and the fixation of carbon in the tissues, do
not constitute a part of it ; on the contrary, the chemical changes that
take place in that substance of the seed, which has been stored up
for the nutrition of the embryo, involve the opposite change, — the
extrication of carbon, which is converted into carbonic acid by unit-
ing with the oxygen of the atmosphere. It is obvious, then, why
light should not only be useless, but even prejudicial, to this process ;
since it tends to fix the carbon in the tissues, which ought to be
thrown off. As soon, however, as the cotyledons or seed-leaves are
unfolded, the influence of light upon them becomes as important, as
it is on the ordinary leaves at a subsequent time ; their surfaces be-
come green, and the fixation of carbon from the atmosphere com-
mences. Up to that point, the young plant is diminishing day by
day (like a plant that is undergoing etiolation), as to the weight of its
solid contents ; although its bulk is increased by the absorption of
water. From the time, however, that its cotyledons begin to act
upon the air, through the stimulus of light, the quantity of solid mat-
ter begins to increase ; and its augmentation subsequently takes place,
at a rate proportional to the amount of green surface exposed, and the
degree of light to which it is subjected.

90. The influence of Light upon the direction of the growing parts
of Plants, upon the opening and closing of flowers, &c., is probably
due to its share in the operations already detailed. Thus the green
parts of Plants, or those which effect the decomposition of carbonic
acid (such as the leaves and stems), have a tendency to grow towards
the light; whilst the roots, through whose dark surfaces carbonic acid
is thrown out by respiration, have an equal tendency to avoid it.
That the first direction of the stems and roots of plants is very much
influenced in this manner, appears from the fact, that, by reflecting
light upon germinating seeds, in such a manner as that it shall only
fall upon them from below, the stems are caused to direct themselves
downwards, whilst the roots grow upwards. There can be no doubt,
however, that Light has also a more direct influence on the develop-
ment of particular organs in certain Vegetables. Thus when the
gemmules* of the Marchantia polymorpha (one of the Hepaticce or
Liverworts) are in process of development, it has been shown by
repeated experiments, that stomata are formed on the side exposed to
the light, and that roots grow from the lower surface ; and that it is
a matter of indifference which side of the little disk is at first turned
upwards, since each has the power of developing stomata, or roots,
according to the influence it receives. After the tendency to the for-
mation of these organs has once been given, however, by the suflS-
ciently prolonged influence of light upon one side, and of darkness

* These geramules are analogous to the buds of higher plants; and they consist of
little collections of cells, arranged in the form of flat disks; which are at first attached
by footstalks to the parent plant, but afterwards fall off", and are developed into new
iadividuals.

I

OF LIGHT AS A VITAL STIMULUS. 69

and moisture upon the other, any attempt to alter it is found to be
vain; for if the surfaces be then inverted, they are soon restored to
their original aspect by the twisting growth of the plant.

91. The same amount of this stimulus is not requisite or desirable
for all Plants ; and we find in the different habitats which are charac-
teristic of different species, even amongst our native plants, that the
amount congenial to each varies considerably. Generally speakings
the succulent thick-leaved Plants require the largest amount ; their
stomata are few in number; and the full influence of light is requisite
to induce sufficient activity in the exhaling process ; accordingly we
find them growing, for the most part, in exposed situations, where
there is nothing to interfere with the full influence of the solar rays.
On the other hand, plants w^ith thinner and more delicate leaves, in
which the exhaling process is easily excited to an excessive amount,
evidently find a congenial home in more sheltered situations ; and
there are some which can only develop themselves in full luxuriance
in the deep shades of a plantation or a forest. By a farther adaptation
of the same kind, some species of Plants are enabled to live and
acquire their green colour, under an amount of deprivation which
would be fatal to most others ; thus in the mines of Freyberg, in which
the quantity of light admitted must be almost infinitesimally small,
Humboldt met with Flowering-Plants of various species ; and Mustard
and Cress have been raised in the dark abysses of the colleries of
this country.

92. Generally speaking, however, the Cryptogamia would seem to
be better adapted than Flowering-Plants, to carry on their vegetating
processes under a low or very moderate amount of this stimulus.
Thus Humboldt found a species of Sea-weed near the Canaries,
which possessed a bright grass-green hue, although it had grown at
a depth of 190 feet in the sea, where, according to computation, it
could have received only l-1500th part of the solar rays that would
have fallen upon it at the surface of the ocean. Many Ferns, Mosses,
and Lichens seem as if they avoided the light, choosing the northern
rather than the southern sides of hedges, buildings, &c., for their resi-
dence; so that the former often present a luxuriant growth of Crypto-
gamic vegetation, whilst the latter are comparatively bare. It must
not be supposed, however, that they avoid light altogether, but only
what is to them an excessive degree of it. The avoidance of light
seems to be much stronger in the Fungi, which grow most luxuriantly
in very dark situations ; and the reason of this is probably to be found
in the fact, that, like the germinating seed, they form rather than de-
compose carbonic acid ; their food being supplied to them from the
decaying substances on which they grow ; and the rapid changes in
their tissues giving rise to a high amount of Respiration, — a change
exactly the converse of that, on which, as we have seen. Light exerts
such a remarkable stimulating power.

93. In regard to the influence of Light upon the functions of Ani-
mals, comparatively little is certainly known. It is evident that the

70 OF LIGHT AS A VITAL STIMULUS.

influence it exerts on those chemical processes, which constitute the
first stage of Vegetable nutrition, can have scarcely any place in Ani-
mals; because they do not perform any such acts of combination, but
make use of the products already prepared for them by Plants. Hence
we do not find that the surface of Animals undergoes that extension,
for the purpose of being exposed to the solar rays, which is so cha-
racteristic a feature in the Vegetable fabric, and so important in its
economy. Still there can be no doubt, that the degree of exposure to
light has a great influence upon the colours of the Animal surface ; and
here we seem to have a manifestation of Chemical agency, analogous
to that which gives colour to the Vegetable surface. Thus it is a mat-
ter of familiar experience, that the influence of light upon the skin of
many persons, causes it to become spotted with hvov^'i\ freckles; these
freckles being aggregations of brown pigment-cells, which either
owed their development to the stimulus of light, or were enabled by
its agency to perform a chemical transformation which they could not
otherwise eflfect. In like manner, the swarthy hue which many per-
sons acquire in warm climates, is due to a development of dark pig-
ment-cells diffused through the epidermis; and an increased develop-
ment of the same kind gives rise to the blackness of the Negro-skin.
There can be no doubt that the prolonged influence of light upon one
generation after another, tends to give a permanent character to this
variety of hue; which will probably be more easily acquired, in pro-
portion to the previously-existing tendency to that change. Thus it
is well known that a colony of Portuguese Jews, which settled at
Tranquebar about three centuries ago, and which has kept itself dis-
tinct from the surrounding tribes, cannot now be distinguished, as to
colour, from the native Hindoos. But it is probable that a similar
colony of fair-skinned Saxons would not, in the same time, have
acquired anything like the same depth of colour in their skins.

94. There can be no doubt that the brilliancy of colour, which is
characteristic of many tribes of animals in tropical climates, espe-
cially Birds and Insects, is in great part dependent, like the bright-
ness of the foliage and fruit of the same countries, upon the brightness
of the light to which their surfaces are exposed. When birds of
warm climates, distinguished by the splendour of their plumage, are
reared under an artificial temperature in our own country, it is uni-
formly observed that they are much longer in acquiring the hues
characteristic of the adult ; and that these are never so bright, as
when they have been produced by the influence of the tropical sun.
And it has been also remarked, that if certain Insects (the Cockroach
for example), which naturally inhabit dark places, be reared in an
entire seclusion from light, they grow up almost as colourless as
Plants that are made to vegetate under similar circumstances.

95. There is abundant proof that Light exercises an important in-
fluence on the processes of development in Animals, no less than in
Plants. Thus, the appearance of Animalcules in infusions of decaying
organic matter is much retarded, if the vessel be altogether secluded

OF LIGHT AS A VITAL STIMULUS. 7X

from it. The rapidity with which the small Entomostracous Crusta-
cea (Water-Fleas, &c.), of our pools, undergo their transformations,
has been found to be much influenced by the amount of light to which
they are exposed. And it has been ascertained that, if equal numbers
of Silk-worm's eggs be preserved in a dark room, and exposed to
common daylight, a much larger proportion of larvae are hatched
from the latter than from the former. — The most striking proof of the
influence of Light on animal development, however, is afforded by
the experiments of Dr. Edwards. He has shown that, if Tadpoles
be nourished with proper food, and be exposed to the constantly-
renewed contact of water (so that their respiration may be freely
carried on, whilst they remain in their Fish-like condition), but be
entirely deprived of light, their growth continues, but their meta-
morphosis into the condition of air-breathing animals is arrested, and
they remain in the condition of large tadpoles. — Numerous facts,
collected from different sources, lead to the belief that the healthy
development of the Human body, and the rapidity of its recovery
from disease, are greatly influenced by the amount of light to which
it has been exposed. It has been observed, on the one hand, that a
remarkable freedom from deformity exists amongst nations who wear
very little clothing ; whilst, on the other, it appears certain that an
unusual tendency to deformity is to be found among persons brought
up in cellars or mines, or in dark and narrow streets. Part of this
difference is doubtless owing to the relative purity of the atmosphere
in the former case, and the want of ventilation in the latter; but
other instances might be quoted, in which a marked variation pre-
sented itself, under circumstances otherwise the same. Thus, it has
been stated by Sir A. Wylie (who was long at the head of the medical
staff* in the Russian army), that the cases of disease on the dark side
of an extensive barrack at St. Petersburgh, have been uniformly,
for many years, in the proportion of three to one, to those on the
side exposed to strong light. And in one of the London Hospitals,
with a long range of frontage looking nearly due north and south, it
has been observed that residence in the south wards is much more
conducive to the welfare of the patients, than in those on the north
side of the building.

96. These facts being kept in view, it is easy to perceive that
there must be differences among the various species of Animals, as
among those of Plants, in regard to the degree of light which is
congenial to them. Among the lowest tribes, in which no special
organs of vision exist, there is evidently a susceptibility to the in-
fluence of light, which appears scarcely to deserve the name of
sensibility, but which seems rather analogous to that which is mani-
fested by Plants ; thus among those Polypes which are not fixed to
particular spots, and amongst Animalcules, there are some species
which seek the light, and others which shun it. And it appears
from various observations upon the depths at which marine animals
are found, especially from the extensive series of facts collected by

72 OF HEAT AS A VITAL STIMULUS.

Prof. E. Forbes,* that there are a series of zones, so to speak, to be
met with in descending from the surface towards the bottom of the
ocean, each of which is characterized by certain species of animals
peculiar to itself, whilst other species have a range through two or
more of the zones ; — the extent of the range of depth, in each species,
bearing a close correspondence with the extent of its geographical
distribution. Now there can be no doubt, that the restriction of
particular species to particular zones is due in great part to the
degree of pressure of the surrounding medium ; but there can be as
little doubt, that the variation in the degree of light also exerts a most
important influence, the solar rays in their passage through sea water
being subject to a loss of one half for every seventeen feet. From
the results of Prof. Forbes' researches, it appears that no species of
Invertebrated animals habitually live at a greater depth than 300
fathoms ; and although Fishes have been captured at a depth of from
500 to 600 fathoms, it is probable that they had strayed from their usual
abodes. It is interesting to remark, that the Proteus anguineus, an
animal which closely corresponds in its fully-developed form with the
transition stage between the Tadpole and the Frog, finds a congenial
abode in the dark lakes of the caverns of Styria and Carniola, and in
the underground caverns that connect them ; — thus showing its adapta-
tion to a condition, which keeps down to the same standard the deve-
lopment of an animal, that is empowered under other circumstances
to advance beyond it.

2. Of Heat, as a Condition of Vital Action.

97. The most perfectly-organized body, supplied with all the other
conditions requisite for its activity, must remain completely inert, if
it do not receive sufficient stimulation from Heat. The influence
which this agent exerts upon living beings, is far more remarkable
than its effects upon inorganic matter ; although the latter are usually
more obvious. We are all familiar with its power of' producing ex-
pansion,— with the liquefaction which is the consequence of its appli-
cation to solids, — with the evaporation which it occasions in liquids,
— and with the enormous repulsive force which it generates among
the particles of vapours; but it is not until we look deeper than the
surface, that we perceive how immediate is the dependence of every
action of Life upon this mysterious agent. The temporary or perma-
nent loss of vitality, in parts of the body subjected to extreme cold,
is a *' glaring instance" of the effect of its withdrawal. This change,
however, is not immediate. Its first step is a mere depression of the
vitality of the part, involving a partial stagnation of the capillary
circulation, diminution of sensibility, and want of muscular power.
But the continued action of cold on the surface, not compensated by
a sufficient generation of heat within, causes the circulation of the

• Report on the Invertebrata of the ^gean Sea, in Transactions of British Associ-
ations, 1843.

t

(

OF HEAT AS A VITAL STIMULUS. 73

part to be completely suspended ; its small vessels contract so that
they become almost emptied of blood, its sensibility and power of
movement are destroyed, — in a word, its vitality is completely sus-
pended. In such a state, a timely but cautious application of warmth
may produce the gradual renewal of the circulation, and the restora-
tion of the other properties of the part, which are dependent upon that
function ; but any abrupt change would complete the mischief which
the cold has begun ; and would altogether destroy, by the violence of
the reaction, the vitality which was only suspended, causing the actual
death of the part. Hence, when the extremities are frost-bitten, no-
thing can be more injurious than to bring them near a fire ; whilst no
treatment has been found so safe and effectual, as the rubbing them
with snow.

98. The influence of Heat upon Vital activity, is attested on a
larger scale, by the striking contrast between the dreary barrenness
of Polar regions, and the luxuriant richness of Tropical countries,
where almost every spot teems with Animal and Vegetable life. And
the alternation of Winter and Summer in temperate climates, may be
almost said to bring under our own view the opposite conditions of
those two extreme cases. The effect of the withdrawal of Heat is
most obvious in the Vegetable kingdom ; since all its operations are
dependent upon a certain supply of that agent ; and in no case are
Plants possessed of the power of generating that supply within them-
selves,— excepting in certain organs which do not impart it to the
rest of the structure. When the temperature of the air falls to the
freezing-point, therefore, we find all the operations of the Vegetable
economy undergoing a complete suspension ; yet a very trifling rise
will produce a renewal of them. It is not only in Evergreens, that
the vital processes continue to be performed to a certain extent during
the winter ; for there is abundant evidence that, even in the trunk and
branches of trees unclothed with leaves, a circulation of sap takes
place, whenever there is even a slight return of warmth. In this
manner, the leaf-buds are gradually prepared during the milder days
of winter, so as to be ready to start forth into full development, with
the returning steady warmth of spring.

99. The influence of Heat upon Vegetation is easily made apparent
by experiment ; in fact experimental illustrations of it, on a large
scale, are daily in progress. For the Gardener, by artificial warmth,
is not only enabled to rear with success the plants of tropical climates,
whose constitution would not bear the chilling influence of our winter ;
but he can also, in some degree, invert the order of the seasons, and
produce both blossom and fruit from the plants of our own country,
when all around seems dead. This process o^ forcing, however, is
unfavourable to the health and prolonged existence of the plants sub-
jected to it; since the period of repose, which is natural to them, is
interrupted; and they are caused, as it were, to live too fast. The
same result occurs, when a plant or tree of temperate climates is
transported to the tropics. Within a very short period after one crop

74 OF HEAT AS A VITAL STIMULUS.

of leaves has fallen off, a new one makes its appearance. This goes
through all its changes of development and decay more rapidly than
it would do in its native clime ; and in its turn falls off, and is speedily
succeeded by another. Hence the fruit-trees of this country, trans-
ported to the East or West Indies, bear abundant crops of leaves, —
three, perhaps, in one year, or five in two years, — but little or no
fruit ; and the period of their existence is much shortened.

100. As Plants are almost wholly dependent upon the temperature
of the surrounding medium, for the supply of Heat necessary for their
growth, many regions must have been devoid of Vegetable life alto-
gether ; if there were not a remarkable adaptation, in the wants of
different species, to the various degrees of temperature of the habita-
tions prepared for them. Thus we see the Cacti and Euphorbise
attaching themselves to the surface of the most arid rocks of tropical
regions, luxuriating, as it would seem, in the full glare of the vertical
sun, and laying up a store of moisture from the periodical rains, of
which even a long-continued drought is not sufficient to deprive them.
The Orchideous tribe, on the other hand, whose greatest develop-
ment occurs in the same zone, find their congenial habitation in the
depths of the tangled forests, where, with scarcely an inferior amount
of heat, they have the advantage of a moister atmosphere, caused by
the exhalations of the trees on which they cling. The majestic Tree-
Fern, again, reaches its full development in insular situations; where,
with a moist atmosphere, it can secure a greater equability of tempe-
rature than is to be met with in the interior of the vast tropical con-
tinents. None of these races can develop themselves elsewhere, to
their full extent, at least, unless their natural conditions of growth are
imitated as far as possible ; and in proportion as this imitation can be
made complete, in that proportion may the plant of the tropics be
successfully reared in temperate regions.

101. There are some examples of the adaptation of particular
forms of Vegetable life to extremes of temperature, which are inte-
resting as showing the extent to which this adaptation may be carried.
In hot springs near a river of Louisiana, of the temperature of from
122° to 145°, there have been seen to grow not merely Confervae
and herbaceous plants, but shrubs and trees ; and a hot-spring in the
Manilla islands, which raises the thermometer to 187°, has plants
flourishing in it, and on its borders. A species of Chara has been
found growing and reproducing itself in one of the hot-springs of
Iceland, which boiled an egg in four minutes ; various Confer vse, &c.,
have been observed in the boiling-springs of Arabia and the Cape of
Good Hope ; and at the island of New Amsterdam, there is a mud-
spring, which, though hotter than boiling-water, gives birth to a
species of Liverwort. On the other hand, there are some forms of
Vegetation, which seem to luxuriate in degrees of cold, that are fatal
to most others. Thus the Lichen, which serves as the winter food
of the Rein-deer, spreads itself over the ground whilst thickly covered
with snow; and the beautiful little Protococcus nivalis j or Red Snow,

OF HEAT AS A VITAL STIMULUS. 75

reddens extensive tracts in the arctic regions, where the perpetual
frost of the surface scarcely yields to the influence of the solar rays at
Midsummer.

102. It is, for the most part, among the Cryptogamic tribes, — the
Ferns, Mosses, Liverworts, Fungi, and Lichens, — that the greatest
power of growing under a low temperature exists ; and we accord-
ingly find that the proportion of these to the Phanerogamia, or
Flowering Plants, increases as we proceed from the Equator towards
the Poles. It has been estimated by Humboldt, that, in Tropical
regions, the number of species of Cryptogamia is only about one-tenth
that of the Flowering Plants ; in the part of the Temperate zone which
lies between Lat. 45° and 52°, the proportion rises to one-half; and
the relative amount gradually increases as we proceed towards the
Poles, until, between Lat. 67° and 70°, the number of species of
Cryptogamia equals that of the Phanerogamia. Among the Flowering
Plants, moreover, the greatest endurance of cold is to be found in
those, which approach most nearly to the Cryptogamia in the low
degree of their development ; thus the Glumaceous group of Endo-
gens, including the Grasses, Rushes, and Sedges, which forms about
one-eleventh of the whole amount of Phanerogamic vegetation in the
Tropics, constitutes one-fourth of it in the Temperate regions, and
one-third in the Polar; and the ratio of the Gymnospermic group of
Exogens, which chiefly consists of the Pine and Fir tribe, increases
in like manner. Still the influence of a high temperature is evident
even upon the Cryptogamia and their allies ; for it is only under the
influence of the light and warmth of tropical climes, that the Ferns,
— the highest among the former, — can develop a woody stem, and
assume the character of trees ; and it is only there that the tall Sugar-
Canes, and the gigantic Bamboos, which are but Grasses on a large
scale, can flourish.

103. It appears, then, that to every species of Vegetable there is
a temperature which is most congenial, from its producing the most
favourable influence on its general vital actions. There is a consi-
derable difference between the power oi growing, and oi flourishing^
at a given temperature. We may lower the heat of a plant to such
a degree, as to allow it to continue to live ; yet its conclition will be
unhealthy. It absorbs food from the earth and air, but cannot assi-
milate and convert it. Its tissue grows but becomes distended with
water, instead of being rendered firm by solid deposits. The usual
secretions are not formed ; flavour, sweetness, and nutritive matter,
are each diminished ; and the power of flowering and producing fruit
is lost. We see a difference in the amount of heat required for the
vegetating processes, even in the various species indigenous to our
own climate ; thus the common Chickweed, Groundsel, and Poa annua
evidently grow readily at a temperature but little above the freezing-
point, whilst the Nettles, Mallows, and other weeds around them,
remain torpid. But the difference is much more strongly marked in
the vegetation of different climates ; showing an evident adaptation

76 OF HEAT AS A VITAL STIMULUS.

of the tribes indigenous to each, to that range of temperature which
they will there experience. Instead of being scantily supplied with
such of the tropical plants as could support a stunted and precarious
life in ungenial climates, the temperate regions are stocked with a
multitude of vegetables which appear to be constructed expressly for
them ; inasmuch as these species can no more flourish at the Equator,
than the equatorial species can in these Temperate regions. And
such new supplies, adapted to new conditions, recur perpetually as
we advance tow^ards the apparently frozen and untenantable regions
in the neighbourhood of the Pole. Every zone has its peculiar vege-
tables ; and while w^e miss some, we find others making their appear-
ance, as if to replace those which are absent.

104. Thus in the countries lying near the Equator, the vegetation
consists in great part of dense forests of leafy evergreen trees. Palms,
Bamboos, and Tree-Ferns, bound together by clustering Orchidea^
and strong creepers of various kinds. There are no verdant meadow^s,
such as form the chief beauty of our temperate regions ; and the lower
orders of Vegetation are extremely rare. It is only in this torrid Zone,
that Dates, Coffee, Cocoa, Bread-fruit, Bananas, Cinnamon, Cloves,
Nutmegs, Pepper, Myrrh, Indigo, Ebony, Logwood, Teak, Sandal-
wood, and many other of the vegetable products, most highly valued
for their flavour, their odour, their colour, or their density, come to
full perfection. As we recede from the Equator, we find the leafy
Evergreens giving place to trees with deciduous leaves ; rich mea-
dows appear, abounding with tender herbs ; the Orchideae no longer
find in the atmosphere, and on the surface of the trees over which
they cluster, a sufficiency of moisture for their support, and the para-
sitic species are replaced by others which grow from fleshy roots
implanted in the soil; but aged trunks are now clothed with Mosses;
decayed vegetables are covered with parasitical Fungi ; and the
waters abound with Confervse. In the warmer parts of the tempe-
rate regions, the Apricot, Citron, Orange, Lemon, Peach, Fig, Vine,
Olive, and Pomegranate, the Myrtle, Cedar, Cypress, and Dwarf
Palm, find their congenial abode. These give place, as we pass
northwards, to the Apple, the Plum, and the Cherry, the Chestnut,
the Oak, the Elm, and the Beech. Going further still, we find that
the fruit-trees are unable to flourish, but the timber-trees maintain
their ground. Where these last fail, we meet \vith extensive forests
of the various species of Firs ; the Dwarf Birches and Willows replace
the larger species of the same kind ; and even near or within the arc-
tic circle, we find wild flowers of great beauty, — the Mezereon, the
yellow and white Water-Lily, and the Globe-flower. Where none of
these can flourish, where trees wholly disappear, and scarcely any
flowering-plants are to be met with, an humbler Cryptogamic vegeta-
tion still raises its head, in proof that no part of the Globe is altogether
unfit for the residence of living beings, and that the empire of Flora
has no limit.

105. But distance from the Equator is by no means the only ele-

OF HEAT AS A VITAL STIMULUS. 77

ment, in the determination- of the mean temperature of a particular
spot, and of the Vegetation which is congenial to it. Its height above
the level of the sea is equally important ; for this produces a variation
in the amount of heat derived from the Sun, at least as great as that
occasioned by difference of latitude. Thus it is not alone on the
summits of Hecla, Mount Blanc, and other mountains of arctic or
temperate regions, that we find a coating of perpetual snow ; we find
a similar covering on the lofty summits of the Himalayan chain, which
extends to within a few degrees of the tropic of Cancer ; and even on
the higher peaks of that part of the ridge of the Andes, which lies
immediately beneath the Equator. The height of the snow-line be-
neath the Equator, is between 15,000 and 16,000 feet above the level
of the sea ; on the south side of the Himalayan ridge, it is as much
as 17,000 feet, but on the north side only 13,000 feet; and in the
Swiss Alps it is about 8000 feet. Its position is very much affected,
however, by local circumstances, such as the neighbourhood of a large
expanse of land or of sea ; hence the small quantity of land in the
Southern Hemisphere, renders its climate generally so much colder
than that of the Northern, that in Sandwich land (which is Lat. 59° S.,
or in the same parallel as the north of Scotland), the whole country,
from the summits of the mountains down to the very brink of the
sea-cliffs, is covered many fathoms thick with everlasting snow ; and
in the island of Georgia (which is in Lat. 54° S., or in the same paral-
lel as Yorkshire,) the limit of perpetual snow descends to the level
of the ocean, the partial melting in summer only disclosing a few
rocks, scantily covered with moss and tufts of grass. Yet the highest
mountains of Scotland, w^hich ascend to an elevation of nearly 5000
feet, and are four degrees more distant from the equator, do not attain
the limit of perpetual snow ; this is reached, however, by mountains
in Norway, at no greater elevation.

106. If, then. Temperature exert such an influence on Vegetation
as has been stated, we ought to find on the sides of lofty mountains
in tropical regions the same progressive alterations in the characters
of the Plants that cover them, as we encounter in journeying from
t^e equatorial towards the polar regions. This is actually the case.
The proportion of Cryptogamia to Flowering Plants, for example, is no
more than one-fifteenth on the plains of the Equatorial region ; whilst
it is as much as one-fifth on the mountains. In ascending the Peak of
Teneriffe, Humboldt remarked as many as five distinct Zones, which
were respectively marked by the products w^hich characterize differ-
ent climates. Thus at the base, the vegetation is altogether tropical ;
the Date-Palm, Plaintain, Sugar-Cane, Banyan, the succulent Eu-
phorbia, the Draccena, and other trees and plants of the torrid zone
there flourish. A little higher grow the Olive, the Vine, and other
fruit-trees of Southern Europe ; there Wheat flourishes ; and there the
ground is covered with grassy herbage. Above this is the woody
region, in which are found the Oak, Laurel, Arbutus, and other beau-
tiful hardy evergreens. Next above is the region of Pines; charac-

78 OF HEAT AS A VITAL STIMULUS.

terized by a vast forest of trees resembling the Scottish Fir, inter-
mixed with Juniper. This gives place to a tract remarkable for the
abundance of Broom ; and at last the scenery is terminated by Scro-
fularia, Viola, a few Grasses, and Cryptogamic plants, which extend
to the borders of the perpetual snow that caps the summit of the
mountain.

107. The effects of Temperature on Vegetation are not only seen
in its influence upon the Geographical distribution of Plants, that is,
in the limitation of particular species to particular climates; for they
are shown, perhaps even more remarkably, in the variation in the size
of individuals of the same species; when that species possesses the
power of adapting itself to widely-different conditions, which is
the case with some. Thus the Cerasus Virginiana grows in the
southern states of North America as a noble tree, attaining one hun-
dred feet in height ; in the sandy plains of the Saskatchawan, it does
not exceed twenty feet ; and at its northern limit, the Great Slave
Lake, in Lat. 62°, it is reduced to a shrub of five feet. Another
curious effect of heat is shown in its influence on the sexes of certain
Monoecious flowers ; thus Mr. Knight mentions that Cucumber and
Melon plants will produce none but male or staminiferous flowers, if
their vegetation be accelerated by heat; and all female or pistillife-
rous, if its progress be retarded by cold.

108. The injurious influence of excessive heat can be, to a certain
extent, resisted by Plants, through the cooling process kept up by the
continual evaporation of moisture from their surface. But the power
of maintaining this cooling process entirely depends upon the supply
of fluid, with which the plant is furnished. If the supply be adequate
to the demand, the effect of heat will be to stimulate all the vital ope-
rations of the plant, and to cause them to be performed with increased
energy ; though, as we have already seen, this energy may be such
as to occasion a premature exhaustion in its powers, by the excessive
luxuriance which it occasions. But if the supply of water be deficient,
the plant is burnt up by the continuance of heat in a dry atmosphere ;
and it either withers and dies, or its tissues become dense and con-
tracted, without losing their vitality. Thus it has been remarked, that
shrubs growing among the sandy deserts of the East, have as stunted
an appearance as those attempting to vegetate in the Arctic regions ;
their leaves being converted into prickles, and their leaf-buds pro-
longed into thorns instead of branches. — The influence of excessive
heat in destroying life, can sometimes be traced through the direct
physical changes which it occasions in the vegetable tissues. Thus
it has been ascertained that grains of corn will vegetate, after exposure
to water or vapour possessing a considerable degree of heat ; provided
that heat do not amount to 144° in the case of water, and 167° in that
of vapour. At these temperatures, the structure of the seed under-
goes a disorganizing change, by the rupture of the vesicles of starch
which form a large part of it ; and the loss of its power of germinating
is therefore readily accounted for. The highest temperature which

OF HEAT AS A VITAL STIMULUS. 79

the soil usually possesses in tropical climates, is about 126°, though
Humboldt has once observed the thermometer rise to 140°. Seeds
imbedded in such a soil, therefore, may not lose their vitality, although
they will not germinate in such temperatures. The temperature most
favourable to germination probably varies in different species, and is
one of the conditions that produces their adaptation to different
climates. Thus it appears that Corn will not germinate in water at a
higher temperature than 95°, whilst Maize will germinate in water at
113° ; and, as is well known, Maize will flourish in countries in which
Corn cannot be grown.

109. We must not confound the power which Plants possess of
vegetating^ or exhibiting vital activity, under widely-different degrees
of temperature, with the power of retaining their vitality in a dormant
condition, which many of them possess in a very remarkable degree.
When the external temperature is much below the freezing-point, it
is impossible that any vegetating processes can go on ; since the Plant
does not possess the power of generating heat within itself. Now
such a complete cessation of activity is quite compatible, in many in-
stances, with the preservation of the organized structure in a condition
perfectly unchanged, and, in consequence, with the continuance of
its peculiar properties ; so that these properties may be again called
into operation, when the temperature shall have risen. But in other
cases, the plant may be killed by the intensity of the cold ; that is, the
return of warmth will not excite it to activity. We have occasion to
notice, in every severe winter, the difference in this respect amongst
the plants which are cultivated in our own climate ; some of them
being killed by a hard frost, the effects of which are resisted by others,
even though their situation be more exposed. In general it will be
found, that the cold acts most powerfully (as might be expected) upon
plants which are not indigenous to our country, but which have been
introduced and naturalized from some warmer regions. But it is
worthy of note, amongst other peculiarities in the relation of Heat and
Vegetation, that many plants are readily killed by a low temperature,
which yet flourish well under a very moderate amount of warmth ; so
that they will grow in situations where the mean temperature of the
year is low and the summers cool, provided the winters are not severe ;
whilst they cannot be preserved without special protection, in situa-
tions where the w^inters are colder, even though the summers should
be much hotter, and the mean temperature of the whole year should be
considerably higher. Thus there are shrubs growing in the Botanic
Garden of Edinburgh, which cannot be safely left in the open air in
the neighbourhood of London, and which would be most certainly
killed by the winter-cold of central France.

110. It does not admit of doubt, that the destructive influence of
a very low temperature upon the Vitality of Plants, is immediately
exerted through its chemical and physical effects upon the tissues and
their contents. Thus it will produce congelation of their fluids ; and
the expansion which takes place in freezing will injure the walls of

80 OF HEAT AS A VITAL STIMULUS.

the containing cells, — distending, lacerating, or even bursting them.
The same cause will probably occasion the expulsion of air from some
parts which ought to contain it ; and the introduction of it into other
parts which ought to be filled with fluid. And a separation will take
place, in the act of freezing, between the constituent parts of the
vegetable juices ; which will render them unfit for discharging their
functions, when returning warmth would otherwise call them into
activity. Hence we are enabled in some degree to account for the
differences in the power of resisting cold, which the various species
of Plants, and even the various parts of the same individual, are found
to possess. For, other things being equal, the power of each plant,
and of each part of a plant, to resist a low temperature, will be in the
inverse ratio of the quantity of water contained in the tissue ; thus, a
succulent herbaceous plant suflfers more than one with a hard woody
stem and dense secretions ; and young shoots are destroyed by a degree
of cold, which does not aflfect old shoots and branches of the same
shrub or tree. Again, the viscidity of the fluids of some plants is an
obstacle to their congelation, and therefore enables them to resist
cold ; thus it is, that the resinous Pines are, of all trees, those which
can endure the lowest temperature. The dimensions of the cells, too,
of which the tissue is composed, appears to have an influence ; the
liability to freeze being diminished by a very minute subdivision of
the fluids. And when the roots are implanted deep in the soil, where
the temperature does not fall so low as that of the surface by many
degrees, the fluidity of the sap may be maintained, in spite of an ex-
tremely cold state of the atmosphere.

111. It is in Cryptogamic plants, that the greatest power of sustain-
ing cold exists; as might be inferred from what has been already stated
in regard to their geographical distribution. The Little Fungus (7b-
Tula Cerevisice) which is one of the principal constituents of Yeast,
does not lose its vitality by exposure to a temperature of 76° below
zero; though it requires a somewhat elevated temperature for its active
growth. It would appear that Seeds are enabled to sustain a degree of
cold without the loss of their vitality, which would be fatal to growing
plants of the same species; thus grains of corn, of various kinds, will
germinate after being exposed for a quarter of an hour to a temperature
equal to that of frozen mercury. It is not diflficult to account for this,
when the closeness of their texture, and the small quantity of fluid
which it includes, are kept in view. The act of Germination, how-
ever, will only take place under a rather elevated temperature ; and
we find in the Chemical changes which it involves, a provision for
maintaining this, w^hen the process has once commenced.

112. The influence of Heat upon the vital activity of Animals, is
quite as strongly marked as we have seen it to be in the case of Plants ;
but the mode in which it is exerted is in many instances very differ-
ent. In those animals which are endowed with great energy of mus-
cular movement, and in which, for the maintenance of that energy, the
nutritive functions are kept in constant activity, we find that a provi-

I

OF HEAT AS A VITAL STIMULUS. 81

sion exists for the development of heat from within, so as to keep the
temperature of the body at a certain uniform standard, whatever may
be the climate in which they live. Their energy and activity are, in
fact, so dependent upon the steady maintenance of a high temperature
in their bodies, that, if this be not kept up nearly to its regular stand-
ard, a diminution or even a complete cessation of vital action takes
place, and even a total loss of vitality may result. In these warm-
blooded animals, as they are termed, we do not so evidently trace the
effects of Heat, because they are constantly being exerted, and because
external changes have but little influence upon them, unless these
changes are of an extreme kind. But if those internal operations, on
which the maintenance of the temperature is dependent, are, from any
cause, retarded or suspended, the effect is immediately visible in the
depressed activity of the whole system. In the class of Birds whose
muscular energy, and whose general functional activity, are greater
and more constant than those of any other animals, the temperature is
pretty steadily maintained at from 108° to 112°; and we shall pre-
sently see, that a depression of the heat of the body to about 80° is
fatal. Among Mammalia, the temperature is usually maintained at
from 98° to 102°; and it seems that here, too, a depression of about
thirty degrees is ordinarily fatal.

113. In the different tribes of Birds and Mammals, we find a very
diversified power of generating heat; and on this depends their adapt-
ation to various climates. Where the usual temperature of the atmo-
sphere is but little below the normal standard ®f the body, a small
amount of the internal calorifying power is required ; and accordingly
we find that animals which naturally inhabit the torrid zone, cannot be
kept alive elsewhere, except, like the Plants of the same regions, by
external heat. On the other hand, the animals of the colder-tempe-
rate and frigid climes are endowed with a much greater internal calo-
rifying power; and their covering is adapted to keep in the heat which
they generate. Such animals (the Polar Bear, for example,) cannot be
kept in health, in the summer of our own country, unless means are
taken for their refrigeration. The constitution of man seems to ac-
quire, by habituation to a particular set of conditions through succes-
sive generations, an adaptation to differences of climate, of which that
of few other animals is susceptible ; and thus we find different races
of human beings inhabiting countries, which are subject to the ex-
tremes of heat and cold. The Hindoo or the Negro, suddenly trans-
ported to Labrador or Siberia during the depth of winter, would pro-
bably sink in the course of a few days, from want of power to generate
within his body a sufficient amount of heat to resist the depressing in-
fluence of the external cold ; whilst, on the other hand, the Esquimaux,
suddenly conveyed to the hottest parts of India or Africa, would
speedily become the subject of disease, which would probably terminate
his life in a short time. It is in the inhabitant of temperate climates,
who is naturally exposed during the seasonal changes of his year, to a
wide range of external temperature, that we find the greatest power of
6

82 OF HEAT AS A VITAL STIMULUS.

sustaining the extremes of either cold or heat; and yet, even in such,
the continued exposure to either extreme during a long series of years,
will so much influence the heat-producing power, that the constitu-
tion does not adapt itself readily to a change of conditions.

114. We see, then, that the variations observable between different
races in this respect, are only exaggerations (so to speak) of the alter-
nations which an individual may undergo in the course of a few years;
and it is easy to understand how such an adaptation may take place to
an increased extent in successive generations; — this being the regular
law, not merely in regard to Man, but in regard to other animals
placed under new conditions, to which they have a certain, but limited,
power of adapting themselves. Thus we find that an European,
who has lived for several years in the East or West Indies, suffers
considerably from the cold, when he first returns to \vinter in his na-
tive country : his constitution having, for a time, lost some of its power
of generating heat. After a few years' residence, however, this power
is commonly recovered to its original extent, unless the age of the
individual be too far advanced; but his children, if they have been
not only born, but brought up, in the hotter climate, experience much
greater difficulty in adapting themselves to the colder one.

115. The conditions on which the power of maintaining the heat
of the body, in despite of external cold, is dependent, will become
the subject of inquiry hereafter (Chap. X). It is sufficient here to
state, that this power is the result of numerous Chemical changes
going on within the body ; and especially of a process analogous to
combustion, in which carbon and hydrogen, taken in as food, are made
to unite with oxygen derived from the atmosphere. It is dependent,
therefore, as to its amount, upon the due supply of the combustible
material on the one hand, and of atmospheric air on the other. If the
former is not furnished, either by the food or by the fatty matter of
the body, (which acts as a kind of reserved store laid up against the
time of need,) the heat cannot be maintained ; and it is in part for
want of power to digest and assimilate a sufficient amount of this
kind of aliment, that animals of warm climates cannot maintain their
temperature in colder regions. On the other hand, if the supply of
oxygen be deficient, as it is when the respiration is impeded by-
diseased conditions of various kinds, there is a similar depression of
temperature.

116. Now, if, from either of these causes, the temperature of the
body of a Bird or Mammal (except in the case of the hyhernating
species of the latter, to be presently noticed) be lowered to about 30°
below its usual standard, not only is there a cessation of vital activity,
but a total loss of \\\.?\ properties ; in other w^ords, the death of the
animal is a necessary result. This occurrence is preceded by a gradu-
ally-increasing torpidity ; which shows the depressing influence of the
cooling process upon the functions in general. The temperature of
the superficial parts of the body is, of course, first affected ; the circu-
lation is at first retarded, causing lividity of the skin ; but, as the tern-

OF HEAT AS A VITAL STIMULUS. 83

perature becomes lower, the blood is almost entirely expelled from
the surface, by the contraction of the vessels, and paleness succeeds.
At the same time, there is a gradually-increasing torpor of the nervous
and muscular systems, which first manifests itself in an indisposition
to exertion of any kind, and then in an almost irresistible tendency to
sleep. At the same time, the respiratory movements become slower,
from the want of the stimulus that should be given by the warm cur-
rent of blood to the medulla oblongata, which is the centre of those
movements; and the loss of heat goes on, therefore, with increased
rapidity, until the temperature of the whole body is so depressed, that
its vitality is altogether destroyed.

117. But when there is a deficiency of the proper animal heat, the
vital activity of the system may be maintained by caloric supplied by
external sources. This fact is of high scientific value, as giving the
most complete demonstration of the immediate dependence of the vital
functions of warm-blooded animals upon a sustained temperature ; and
its practical importance can scarcely be overrated. It rests chiefly
upon the recent experiments of Chossat, who had in view to determine
the circumstances attending death by Inanition or starvation. He
found that, when Pigeons were entirely deprived of food and w^ater,
their average temperature underwent a tolerably regular diminution
from day to day ; so that, after several days, (the exact number vary-
ing with their previous condition,) it was about 4^° lower than at first.
Up to this time, it seems that the store of fat laid up in the body sup-
plies the requisite material for the combustive process ; so that no very
injurious depression of temperature occurs. But, as soon as this is
exhausted, the temperature falls rapidly, from hour to hour; and as
soon as the total depression has reached 29^° or 30°, death super-
venes. Yet it was found by M. Chossat, that when animals thus
reduced by starvation, w^hose death seemed impending, (death actually
taking place, in many instances, whilst the preliminary processes of
weighing, the application of the thermometer, &c., were being per-
formed,) were subjected to artificial heat, they were almost uniformly
restored, from a state of insensibility and want of muscular power, to
a condition of comparative activity. Their temperature rose, their
muscular power returned, they took food when it was presented to
them, and their secretions were renewed ; and, if this artificial assist-
ance was sufficiently prolonged, and they were supplied \vith food,
they recovered. If the heat was withdrawn, however, before the time
when the digested food was ready, in sufficient amount, to supply the
combustive process, they still sank for want of it.

118. Various important practical hints may be derived from the
consideration of these facts. There can be no doubt that, in many
diseases of exhaustion, the want of power to sustain the requisite
temperature, is the immediate cause of death ; the whole combustible
material of the body having been exhausted, and the digestive appa-
ratus not being able to supply what is required. Now where this is
the case, there is no doubt that life may be prolonged, and that

84 OF HEAT AS A VITAL STIMULUS.

recovery may be favoured, by the judicious sustentation of the tem-
perature of the body. This may be effected either by internal or by
external means. Of the internal, the most efficient is undoubtedly
the administration of alcoholic fluids; which, for reasons hereafter to
be given, (§ 496,) will be absorbed into the circulating system, when
no other alimentary substance can be taken in; and w^hich, moreover,
exert a favourable influence by their specific stimulating effect upon
the nervous system. It is a matter of familiar experience, that in
such conditions of the body, the quantity of alcohol which may be
administered with positive and evident benefit, is such as w^ould in
ordinary circumstances be productive of the most injurious results;
and this is fully accounted for by the reflection, that it is burnt off as
fast as it is taken in. But a most important adjunct in all such cases,
— and in many instances a substitute for alcohol, when the latter
w^ould be inadmissible, — will be found in the application of external
heat ; and especially in the subjection of the whole surface to its in-
fluence, by means of the hot-air bath. This is a valuable portion of
the treatment, in the recovering of persons who have been reduced
to insensibility by suffocation of any kind; and especially in cases of

Irowning, since the heat of the body is rapidly withdrawn by the
conducting power of the water. Indeed it may be stated as a general
rule, that, where the temperature of the body is lowered from any

ause, external heat may be advantageously applied ; and much evi-
dence has lately been produced to show, that the reparative processes
by which extensive wounds are healed, go on more favourably under
the contact of warm, dry air, than with any other application.

119. On the other hand, where the object is to keep dow^n a ten-
dency to a too violent action, the local application of moderate cold
is found to be of the greatest value ; all surgeons of eminence being
now agreed upon the efficacy of water- dressing in restraining the in-
flammatory process, especially in cases of wounds of the joints, in
which this action is most to be apprehended. The general applica-
tion of cold to the surface, by means of continued exposure to cool
air, or by a short immersion in cold water, is frequently in the highest
degree beneficial, by imparting tone to the system, i.e., by producing
a firmer condition in the solids w^hich were previously relaxed, and
more especially by calling into action the tonicity of the walls of the
blood-vessels, wdiich imparts to them an increased resistance, and thus
favours the regular and vigorous circulation of blood, upon principles
which will be hereafter stated (§ 609). But so far from producing
any permanent depression in the temperature of the body, this mea-
sure has a tendency to elevate it, by the increased vigour it produces
in the circulation ; hence the glow which is experienced after the
use of the cold bath. If this effect be not produced, and a chilling
of the body, instead of an invigorating warmth, be the result of the
use of cold, it is evident that this cannot be beneficial. The inju-
rious results of the too-prolonged application of even a moderate
degree of cold, are seen in the depression of temperature, without a

OF HEAT AS A VITAL STIMULUS. S&

corresponding reaction, which is the consequence of an immersion in
water of 50° or 55° prolonged for several hours ; and still more in
that chilling of the whole surface frequently productive of the most
serious consequences, which arises from the evaporation of fluid from
garments that have been moistened, either by perspiration from with-
in, or by the fall of rain or dew upon their exterior. There is no
doubt that the obstruction to the continuance of the perspiration,
presented by a covering already saturated with moisture, is one cause
of the injurious results that so commonly follow such an occurrence;
but there is as little doubt that the chilling influence of the external
evaporation has a large share in producing them. For experience
shows that, if the evaporation be prevented by an impenetrable
covering, the contact of a garment thoroughly saturated with mois-
ture is not productive of the same injurious consequences.

120. The practical importance of the due comprehension of the
principles upon which heat and cold should be employed, in the
treatment of disease and the preservation of health, has required
this digression. We now proceed to consider the influence of
temperature upon a certain group of warm-blooded animals ; which
offers a remarkable peculiarity in this respect, — their power of gene-
rating heat being for a time greatly diminished or almost completely
suspended ; the temperature of their bodies following that of the
air around, so that it may be brought down nearly to the freezing-
point ; their general vital actions being carried on with such feeble-
ness as to be scarcely perceptible ; and yet the vital properties of
the tissues being retained, so that, when the temperature of the body
is again raised, the usual activity returns. This state, which is
called hybernation, appears to be as natural to certain animals, as
sleep is to all ; and it corresponds with sleep in its tendency to
periodical return.

121. No account can be given of the causes to which it is due;
but the condition of the animals presenting it offers several points of
much interest. There are some, as the Lagomys, in which it appears
to differ but little from deep ordinary sleep ; they retire into situations
which favour the retention of their warmth ; and they occasionally
wake up, and apply themselves to some of the store of food, which
they have provided in the autumn. In other cases, a great accumu-
lation of fat takes place within the body in autumn, favoured by the
oily nature of the seeds, nuts, &c., on which the animals then feed ;
and this serves the purpose of maintaining the temperature for a suf-
ficient length of time, not indeed to the usual standard, but to one
not far below it. The state of torpor in these animals is more pro-
found than that of deep sleep, but it is not such as to prevent them
from being easily aroused ; and their respiratory movements, though
diminished in frequency, are still performed without interruption.
But in the Marmot, and in animals which, like it, hybernate com-
pletely, the temperature of the body (owing to the want of internal
power to generate heat) and the general vital activity, are proper-

86 OF HEAT AS A VITAL STIMULUS.

tionably depressed ; the respiratory movements fall from 500 to 14
per hour, and are performed without any considerable enlargement of
chest ; the pulse sinks from 150 to 15 beats per minute ; the state
of torpidity is so profound that the animal is with difficulty aroused
from it ; and the heat of the body is almost entirely dependent upon
the temperature of the surrounding air, not being usually more than
a degree or two above it. When the thermometer in the air is
somewhat below the freezing-point, that placed within the body falls
to about 35° ; and at this point it may remain for some time without
any apparent injury to the animal, as it revives when subjected to a
higher temperature. When, however, the body is exposed to a more
intense degree of cold, the animal functions undergo a temporary re-
newal ; for the cold seems to act like any other stimulus in arousing
them. The respiratory movements and the circulation increase in ac-
tivity, so as to generate an increased amount of heat ; but this amount
is insufficient to keep up the temperature of the body, which is at last
depressed to a degree inconsistent with the maintenance of life ; and
not only the suspension of activity, but the total loss of vital proper-
ties is the result.

122. Now the condition of a hybernating Mammal closely resem-
bles that of a cold-blooded animal, in regard to the dependence of its
bodily temperature upon external conditions. There is this important
difference, however ; — that the reduction of the temperature of the
former to 60*^ or 50° is incompatible with a state of activity, which
is only exhibited when the temperature rises to nearly the usual Mam-
malian standard ; — whilst a permanently low or moderate temperature
is natural to the bodies of most cold-blooded animals, whose func-
tions could not be well carried on under a higher temperature. Thus
all the muscles of a Frog are thrown into a state of permanent and
rigid contraction, by the immersion of its body in water no warmer
than the blood which naturally bathes those of the Bird ; and we find,
accordingly, that cold-blooded animals which cannot sustain a high
temperature, are provided with 2i frigorifying rather than with a calo-
rifying apparatus. Although we are accustomed to rank all animals,
save Birds and Mammals, under the general term cold-blooded, yet
there exist among them considerable diversities as to the power of
generating heat within themselves, and of thus rendering themselves
independent of external variations. Thus among Reptiles, it appears
that there are some which can sustain a temperature several degrees
above that of the atmosphere, especially when the latter is sinking ;
and among Fishes it is certain that there are species, — the Tunny and
Bonifo, for example, — which are almost entitled to the name of warm-
blooded animals, their temperature being kept up to nearly 100°,
when that of the sea is about 80°. It is uncertain, however, to what
extent it would be depressed, by a lowering of that of the surround-
ing medium. The greatest power of developing heat in cold-blooded
animals appears to exist, when their bodies are reduced nearly to the
freezing-point, and when that of the surrounding air or water is much

OF HEAT AS A VITAL STIMULUS. 87

below it. Thus Frogs have been found alive in the midst of ice
whose temperature was as low as 9°, the heat of their own bodies
being 33° ; and it has been observed that even Animalcules contained
in water that is being frozen, are not at once destroyed, but that each
lives for a time in a small uncongealed space, where the fluid seems
to be kept from solidifying by the caloric liberated from the Animal-
cule.

123. The peculiar condition of the class of Insects, in regard to its
heat-producing power, exhibits in a very striking manner the con-
nection between an elevated temperature and vital activity. In the
Larva state of Insects, the temperature of the animal follows closely
that of the surrounding air, as in the cold-blooded classes generally ;
but it is usally from \^ to 4° above it. In the Pupa condition, which
is one of absolute rest in all insects that undergo a complete meta-
morphosis, the temperature scarcely rises above that of the surround-
ing medium ; except nearly at the close of the period, when it is
about to burst its envelops and to come forth as the perfect Insect.
The elevation of temperature which different Insects present, varies
in part according to the species, and in part with the condition of the
individual in regard to rest or activity ; but the same principle is evi-
dently operating in both cases, since the variation existing amongst
diflferent species, in regard to their heat-producing power, is closely
connected with the amount of activity natural to them. The highest
amount is to be found in the industrious Hive-Bee and its allies, and
in the elegant and sportive Butterflies, which are almost constantly on
the wing in search of food ; next to these come the Beetles of active
flight ; and lastly those which seldom or never raise themselves upon
the wing, but pursue their labours on the ground. The temperature
of individual Bees has been found to be about 4° above that of the
atmosphere, when they are in a state of repose ; but it rises to 10° or
15° when they are excited to activity. When they are aggregated
together in clusters, however, the temperature which they possess is
often as much as 40° above that of the atmosphere. When reduced
to torpidity by cold, they still generate heat enough to keep them from
being frozen, unless the cold be very severe ; and they may be
aroused by moderate excitement to a state of activity, in which the
temperature rises to a very considerable height. Now although the
increased production of heat is in these cases, as in hybernating Mam-
mals, similarly aroused, the consequence of the increased activity, there
can be no question that it is a condition necessary to the continuance
of that activity ; since we find that, if the temperature of the body be
again reduced by external cold, the activity cannot be long main-
tained.

124. Whilst the foregoing facts exhibit the connection between an
elevated temperature, and the most active condition of the muscular
and nervous systems, in cold-blooded animals, there is abundant evi-
dence of the same kind in regard to the influence of heat upon the
processes of nutrition and development. Thus the time of emersion

88 OF HEAT AS A VITAL STIMULUS.

of Insect-larvse from their eggs, — or in other words, the rate at which
the previous formative processes go on, is entirely dependent upon
the temperature. In the case of the Bird we find that, if the tempe-
rature be not sufficient to develop the egg, chemical changes soon
take place, which involve the loss of its vitality ; or if the tempera-
ture be reduced so low as to prevent the occurrence of those changes,
the loss of heat is in itself destructive of life. But this is not the case
in regard to the eggs of cold-blooded animals in general ; for, like the
beings they are destined to produce, they may be reduced to a state
of complete inaction by a depression of the external temperature ;
whilst a slight elevation of this renews their vital operations, at a rate
corresponding to the warmth supplied. Hence the production of lar-
vae from the eggs of Insects may be accelerated or retarded at plea-
sure ; and this is, in fact, practised in the rearing of Silk-worms, in
order to adapt the time of their emersion from the egg to the supply
of food which is ready for them. The same may be said in regard to
the eggs of other cold-blooded animals; those, for example, of the
minute Entomostracous Crustacea (Water-Fleas, &c.,) which people
our ditches and ponds. In many of these, the race is continued
solely by the eggs, which remain dormant through the winter ; all the
parents being destroyed by the cold. The common Daphnia pulex
produces two kinds of eggs; from one, the young are very speedily
hatched: but the others, which are produced in the autumn, and en-
veloped in a peculiar covering, do not give birth to the contained
young until the succeeding spring. They may be at any time hatched,
however, by artificial warmth.

125. We sometimes find special provisions, for imparting to the
eggs a temperature beyond that which is natural to the bodies of the
parents; thus it has been lately shown that in Serpents, the tempera-
ture of the posterior part of the body rises considerably, when the
eggs are lying in the oviduct, preparatory to being discharged, —
evidencing a special heat-producing power in the surrounding parts
at this period, which is obviously for the purpose of aiding the matu-
rity of the eggs. The Viper, whose eggs are frequently hatched in
the maternal oviduct, so that the young are brought forth alive, is
occasionally seen basking in the sun, in such a position as to receive
its strongest heat on the parts that coverthe oviduct. Certain Birds
have recourse to substitutes for the usual method of incubation. The
Tallegalla of New Holland is directed by its remarkable instinct, not
to sit upon its eggs, but to bring them to maturity by depositing them
in a sort of hot-bed, which it constructs of decaying vegetable matter.
The Ostrich is believed to sit upon its eggs, when the temperature falls
below a certain standard, but to leave them to the influence of the solar
heat when this is sufficient to bring them to maturity; and this state-
ment derives confirmation from a similar fact observed in a Fly-
catcher, which built in a hot-house during several successive years,
— the bird quitting its eggs when the temperature w,as high, and
resuming its place when it fell. In all these cases, as in many more

OF HEAT AS A VITAL STIMULUS. 89

which might be enumerated, we observe the influence of an elevated
temperature upon the processes of development; and the provisions
made by Nature, in the physical or mental constitution of animals,
for affording that influence. The development of heat around the
oviduct of the Serpent is a process over which the individual has
no control, being entirely dependent upon certain Organic changes;
whilst the imparting of warmth to its eggs by the Bird, either from
its own body or through artificial means, is committed to the guidance
of its Instinct, — which same instinct leads it to suspend the process
when it is not necessary.

126. Phenomena of an equally interesting and instructive charac-
ter may be observed in the history of the Pupa state of Insects ; which,
in those that undergo a complete metamorphosis, may be almost cha-
racterized as a re-entrance into the egg. In fact we shall obtain the
most correct idea of the nature of that metamorphosis, by considering
the Larva as an embryo, which comes forth from the egg in a very
early and undeveloped condition, for the sake of obtaining materials
for its continued development, which the egg does not supply in
sufficient amount. When these have been digested and stored up in
the body, the animal becomes completely inactive, so far as regards
its external manifestations of life ; and it forms some kind of envelop
for its protection, which may not be unaptly compared to the shell or
horny covering of the egg. Within this are gradually developed the
wings, legs, and other parts which are peculiar to the perfect Insect ;
whilst even those organs, which it possesses in common with the
Larva, are for the most part completely altered in character. When
this process of development is completed, the Insect emerges from
its Pupa case, just as the Bird comes forth from the egg ; then only
does its Insect life begin, its previous condition having been that of
a Worm; and the alteration of its character is just as evident in its
instinctive propensities, as it is in its locomotive and sensorial powers.

127. Now this process of development is remarkably influenced
by external temperature ; being accelerated by genial warmth, and
retarded by cold. There are many Larvae, which naturally pass into
the Pupa state during the autumn, remain in it during the entire
winter, and emerge as perfect Insects with the return of spring. It
was found by Reaumur, that Pupse, which would not naturally have
been disclosed until May, might be caused to undergo their meta-
morphosis during the depth of winter, by the influence of artificial
heat ; whilst, on the other hand, their change might be delayed a
whole year beyond its usual time, by the prolonged influence of a
cold atmosphere. In order to hasten the development of the pupse
of the Social Bees, a very curious provision is made. There is a
certain set, to which the name of Nurse-bees has been given, whose
duty it is to cluster over the cells in which the Nymphs or Pupse are
lying, and to communicate the heat to them, which is developed by
the energetic movements of their own bodies, and especially by respi-
ratory actions of extreme rapidity. The nurse-bees begin to crowd

90 OF HEAT AS A VITAL STIMULUS.

upon the cells of the nymphs, about ten or twelve hours before these
last come forth as perfect Bees. The incubation (for so it may be
called) is very assiduously persevered in during this period by the
Nurse-bees ; when one quits the cell, another takes its place ; and
the rapidity of the respiratory movements increases, until they rise to
130 or 140 per minute, so as to generate the greatest amount of
heat just before the young bees are liberated from the combs. In
one instance, the thermometer introduced among seven nursing-bees
stood at 92^° ; the temperature of the external air being 70°. We
observe in this curious propensity a manifest provision for accelera-
ting the development of the perfect Insect, which requires (as already
pointed out) a higher temperature than the larva, in virtue of its
greater activity. The Nurse-bees do not station themselves over the
cells which are occupied by the larvae ; nor do they incubate the
nymph-cells with any degree of constancy and regularity, until the
process of development is approaching its highest point.

128. We have seen that the animals termed cold-blooded are
greatly influenced as to the temperature of their bodies, by the tem-
perature of the surrounding medium ; although many of them are
endowed with the power of keeping themselves a certain number of
degrees above it. Now the consequence of this is, that all of them
which are subject to any considerable and prolonged amount of cold,
pass into a state of more or less complete inactivity during its con-
tinuance ; which state bears a close correspondence with the hyber-
nation of certain Mammalia. Among the Reptiles of cold and tem-
perate countries, this torpid state uniformly occupies a considerable
part of the year ; as it does also with Insects, terrestrial Mollusks,
and other Invertebrated animals, which are subject to the influence
of the cold. On the other hand. Fishes, Crustacea, and other ma-
rine animals, do not usually appear to pass into a state of torpidity;
the temperature of the medium they inhabit never undergoing a
degree of depression nearly so great as that of the atmosphere.
The amount of change necessary to produce this effect, or on the
other hand to call the animals from a state of torpidity to one of
active energy, differs for different species ; and there is probably a
considerable difference even among individuals of the same species,
according to the temperature*under which they habitually live. Thus
one animal may remain torpid under a degree of warmth which will
be sufficient to arouse another of the same kind accustomed to a
somewhat colder climate ; because the stimulus is relatively greater to
the latter.

129. It was observed by Mr. Darwin, that at Bahia Blanca, in
South America, the first appearance of activity in animal and vegeta-
ble life, a few days before the vernal equinox, presented itself under
a mean temperature of 58°, the range of the thermometer in the
middle of the day being between 60° and 70°. The plains were
ornamented by the flowers of a pink wood-sorrel, wild peas, evening
primroses, and geraniums ; the birds began to lay their eggs, numer-

OF HEAT AS A VITAL STIMULUS. 91

ous beetles were crawling about ; and lizards, the constant inhabit-
ants of a sandy soil, were darting about in every direction. Yet a
few days previously, it seemed as if nature had scarcely granted a
living creature to this dry and arid country; and it was only by dig-
ging in the ground that their existence had been discovered, — several
insects, large spiders, and lizards, having been found in a half torpid
state. Now at Monte Video, four degrees nearer the Equator, the
mean temperature had been above 58° for some time previously, and
the thermometer rose occasionally during the middle of the day, to
69° or 70° ; yet with this elevated temperature, almost equivalent
to the full summer heat of our own country, almost every beetle,
several genera of spiders, snails, and land-shells, toads and lizards,
were still lying torpid beneath stones. We have seen that at Bahia
Blanca, whose climate is but a little colder, this same temperature,
with a rather less extreme heat, was sufficient to awake all orders of
animated beings; — showing how nicely the required degree of stimu-
lus is adapted to the general climate of the place, and how little it
depends on absolute temperature.

130. We may learn much from the Geographical distribution of
the different species of cold-blooded animals, in regard to the influence
of temperature on Animal life. No general inferences of this kind
can be founded upon the distribution of warm-blooded animals ; since''
their own heat-evolving powers make them in great degree inde-
pendent of external warmth. And it is probably from the distribu-
tion of the marine tribes, whose extension is less influenced by local
peculiarities, that the most satisfactory deductions are to be drawn.
In regard to the class of Crustacea, which is the one that has been
most fully investigated in this respect, the following principles have
been pointed out by M. Milne Edwards ; and they are probably more
or less applicable to most others.

I. The varieties of form and organization manifest themselves more,
in proportion as we pass from the Polar Seas towards the Equator. —
Thus on the coast of Norway, where there is frequently a vast multi-
plication of individuals of the same species, the number of species is
very small ; but the latter increases rapidly as we go southwards.
Thus the number of species of Crustacea of the two highest Orders,
known to exist on the coast of Norway and in the neighbouring
seas, is only 16 ; but 82 are known to be the inhabitants of the wes-
tern shores of Britain, France, Spain, and Portugal; 114 are known
in the Mediterranean Sea ; and 202 in the Indian Ocean. A similar
increase may be observed in following the coast of the New World,
from Greenland to the Caribbean Sea.

II. The differences of form and organization are not only more nu-
merous and more characteristic in the warm than in the cold regions of
the globe; they are also more important. — The number of natural
groups, which we find represented in the polar and temperate re-
gions, is much smaller than that, of which we find types or examples
in the tropical seas. In fact, nearly all the principal forms which

92- OF HEAT AS A VITAL STIMULUS.

are met with in colder regions, also present themselves in warm ; but
a very large proportion of the latter have no representatives among
the former. Of the three primary groups composing the Class, in-
deed, one is altogether wanting beyond the 44th degree of latitude ;
and in the other two there are whole Orders, as well as numerous
subordinate divisions, which are as completely restricted to the war-
mer seas.

III. JYot only are those Crustacea^ which are most elevated in the
scale^ deficient in the Polar regions ; but their relative number increases
rapidly as we pass from the Pole towards the Equator. — Thus the
Brachyoura,*^ which must be considered as the most elevated of the
whole series, are totally absent in some parts of the arctic region ; and
we find their place tak;en by the far less complete Edriophthalma,
with a small number of Anomourous and Macrourous Decapods. In
the Mediterranean, however, the Decapods surpass the Edriophthal-
ma in regard to the number of species; and the Brachyourous division
of the former predominates over the Macrourous, in the proportion
of two to one. And in the East and West Indies, the species of
Brachyoura are to those of Macroura, as three, four, or even five, to
one. Again, the Land Crabs, which are probably to be regarded as
taking the highest rank among the Brachyoura (and therefore in the
entire class), are only to be met with between the tropics. Moreover,
of the fluviatile Decapods (inhabiting rivers, brooks, and fresh-water
lakes,) a large proportion belong, in tropical regions, to the elevated
type of the Brachyoura ; whilst all those found in the temperate and
arctic zones (the River Cray-fish and its allies) belong to the Macrou-
rous division.

IV. When we compare together the Crustacea of different parts of
the world, we observe that the average size of these animals is consider-
ably greater in tropical regions, than in the temperate or frigid climes. —
The largest species of the arctic and antarctic seas are far smaller than
those of the tropical ocean ; and they bear a much smaller proportion
to the whole number. Further, in almost every natural group, we
find that the largest species belong to the equatorial regions; and that
those which represent them (or take their place, as it were,) in tempe-
rate regions, are of smaller dimensions.

V. It is where the species are most numerous and varied, and where
they attain the greatest size, in other words, where the temperature is
most elevated, — that the peculiarities of structure which characterize the
several groups are most strongly manifested. Thus the transverse de-
velopment of the cephalo-thorax, which is so remarkable in the Bra-
chyourous Decapods (the breadth of the carapace or arched shell in the
typical Crabs being much greater than its length from back to front), is
carried to its greatest extent in certain Crustacea of the Equatorial re-

* The DECAronA or ten-footed Crustaceans constitute the highest or most perfectly
organized Order of the class. This Order is composed of the Brachyoura (short-
tailed) or Crabs; of the Macroura (long-tailed) or Lobsters, Shrimps, &c.; and of the
Anonioura (dissimilar-tailed) or Hermit-Crabs, &c.

OF HEAT AS A VITAL STIMULUS. 93

gion ; and the same might be said of the characteristic peculiarities of
most other natural groups. Further, it is in this region that we find
the greatest number of those anomalous forms, which depart most
widely from the general structure of the Class.

VI. Lastly, there is a remarkable coincidence between the temperature
of different regions, and the prevalence of certain forms of Crustacea. —
Thus there are few genera to be met with in the West Indian seas
which have not their representatives in the East Indian, — the species,
however, being usually different. The same may be said of the genera
inhabiting the temperate regions of the globe ; — similar generic forms
being usually met with in the corresponding parts of the Old and New
World, and of the Northern and Southern Hemispheres, although the
species are almost invariably different.

131. Now although, as appears from the foregoing general state-
ments, the number of species of Crustacea inhabiting the colder seas
bears a very small proportion to that which is found within the tro-
pics, and although the species formed to inhabit cold climates are so
far inferio-r, both as to size and as to perfection of development, yet it
does not follow that the same proportion exists in regard to the rela-
tive amount of Crustacean life in the two regions: for this depends
upon the multiplication of individuals. In fact it may be questioned
whether there is any inferiority in this respect; so abundant are some
of the smaller species in the Arctic and Antarctic, as well as in the
Temperate seas. Thus we see that a low range of temperature is as
well adapted to sustain their life, as a higher range is to call forth those
larger and more fully developed forms, which abound in the tropical
ocean. This is an obvious reason why the seas of the frigid zones
should be much more abundantly peopled than the land; the mean
temperature of the former being much higher. And it would almost
seem as if Nature had intended to compensate for the dreariness and
desolation of the one, by the profuseness of life which she has fitted
the other to support.

132. The influence of Temperature in modifying the size of indi-
vidual Animals of the same species, is not so strongly marked as it is
in the case of Plants; for this reason, perhaps, that an amount of con-
tinued depression or elevation, which might be sustained by a Plant,
but which w^ould exert a modifying influence upon its growth, would
be fatal to an animal formed to exist in the same climate. Instances are
not w^anting, however, in which such a modifying influence is evident;
and these, as might be anticipated, are to be met with chiefly among
the cold-blooded tribes. Thus the Bulimus rosaceus, a terrestrial Mol-
lusk, is found on the mountains of Chili of so much less a size than
that which it attains on the coast, as to have been described as a dis-
tinct species. And the Littorina petraa, found on the south side of
Plymouth Breakwater, acquires, from its superior exposure to light
and heat (though, perhaps, also from the greater supply of nutriment
which it obtains), twice the size common to individuals living on the
north side within the harbour. The following circumstance show^sthe

94 ' OF HEAT AS A VITAL STIMULUS.

favourable influence of an elevated temperature, in producing an un-
usual prolificness in Fish ; which must be connected with general vital
activity. Three pairs of Gold-fish were placed, some years since, in
one of the engine-dams or ponds common in the manufacturing dis-
tricts, into which the water from the engine is conveyed for the pur-
pose of being cooled; the average temperature of such dams is about
80°. At the end of three years the progeny of these Fish, which
were accidentally poisoned by verdigris mixed with the refuse tallow
from the engine, were taken out by wheelbarrows-full. It is not
improbable that the unusual supply of aliment, furnished by the re-
fuse grease that floats upon these ponds (which would impede the
cooling of the water, if it w^ere not consumed by the Fish), contri-
buted w^ith the high temperature to this unusual fecundity.

133. The influence of variations in the Heat of the body upon its
vital activity, is further manifested by the very remarkable experi-
ments of Dr. Edwards, who has shown that cold-blooded animals live
much faster (so to speak) at high temperatures than at low^ ; so that
they die much sooner when deprived of other vital stimuli. Thus when
Frogs w^ere confined in a limited quantity of w^ater, and were not per-
mitted to come to the surface to breathe, it w^as found that the dura-
tion of their lives was inversely proportioned to the degree ofheatof the
fluid. Thus when it was cooled dowm to the freezing point, the frogs
immersed in it lived during from 367 to 498 minutes. At the tempe-
rature of 50°, the duration of their lives w'as from 350 to 375 minutes;
at 72°, it was from 90 to 35 minutes ; at 90°, from 12 to 32 minutes ;
and at 108°, death was almost instantaneous. The prolongation of life
at the lower temperatures w^as not due to torpidity, for the animals
perform the functions of voluntary motion, and enjoy the use of their
senses; but it is occasioned by their diminished activity, which occa-
sions a less demand for air. On the other hand, the elevation of tem-
perature increases the demand for air, and causes speedier death when
it is withheld, by increasing the general agility. The natural habits of
these animals are in correspondence with these facts. Duringthe winter,
the influence of a sufficient amount of aerated water upon their exte-
rior serves to maintain the required amount of respiration through the
skin, so that they are not obliged to come to the surface to take in air
by the mouth. As the season advances, however, their activity in-
creases, a larger amount of respiration is required, and the animals are
obliged to come frequently to the surface to breathe. During summer
the yet higher temperature calls forth an increased energy and activity
in all the vital functions; the respiration must be proportionably in-
creased ; the action of the air upon the cutaneous surface, as well as
upon the lungs, is required ; and if the animals are prevented from
quitting the water to obtain this, they die as soon as the warmth of
the season becomes considerable.

134. The result of experiments on Fishes, in regard to the depri-
vation or limited supply of the air contained in the water in which
they are immersed, is exactly similar ; the duration of life being in-

OF HEAT AS A VITAL STIMULUS. 95

versely as the temperature. And precisely the same has been ascer-
tained with respect to hybernating Mammals ; which, as already
remarked, are for a time reduced, in all such conditions, to the level
of cold-blooded animals.

135. Conformably to the same principle, we find that cold-blooded
animals are enabled to sustain the deprivation of food during a much
longer period, at cold temperatures, than at warm. The case is pre-
cisely the reverse in regard to most warm-blooded animals ; since in
them a due supply of food is a condition absolutely necessary (as we
have already seen) for the maintenance of that amount of bodily heat,
whose loss is fatal to them ; and exposure to a low temperature w^ill
of course more speedily bring about that crisis. Hence it is that Cold
and Starvation combined are so destructive to life. But in this respect,
also, the hybernating Mammals correspond with the cold-blooded
classes ; their power of abstinence being inversely as the temperature
of their bodies.

136. Although a very low temperature is positively inconsistent
with the continuance of vital activity^ in Animals as in Plants, yet
we find that even very severe cold is not necessarily destructive of
the vital properties of organized tissues ; so that, on a restoration of
the proper amount of heat, their functions may continue as before.
Of this we have already noticed an example, in the case of frost-bitten
limbs ; but the fact is much more remarkable, when considered in
reference to the whole body of an animal, and the complete suspen-
sion of all its functions. Yet it is unquestionably true, not only of the
lowest and ^simplest members of the Animal kingdom, but also of
Fishes and Reptiles. In one of Captain Ross's Arctic Voyages,
several Caterpillars of the Laria Rossii having been exposed to a
temperature of 40° below zero, froze so completely, that, when thrown
into a tumbler, they chinked like lumps of ice. When thawed, they
resumed their movements, took food, and underwent their transform-
ation into the Chrysalis state. One of them, which had been frozen
and thawed four times, subsequently became a Moth. The eggs of the
Slug have been exposed to a similar degree of cold, without the loss
of their fertility. It is not uncommon to meet, in the ice of rivers,
lakes, and seas, with Fishes which have been completely frozen, so
as to become quite brittle ; and which yet revive when thawed. The
same thing has been observed in regard to Frogs, Newts, &c.; and
the experiment of freezing and subsequently thawing them, has been
frequently put in practice. Spallanzani kept Frogs and Snakes in an
ice-house for three years ; at the end of which period they revived on
being subjected to warmth.

137. It does not appear, however, that the same capability exists,
in regard to any warm-blooded animals ; since if a total suspension*
of vital activity take place in the body of a Bird or Mammal for any

* In the case of hybernating Mammals, the suspension is not total; and if it be
rendered such, the same result follows as in other instances.

.$§ OF HEAT AS A VITAL STIMULUS. ^

length of time, in consequence of the prolonged application of severe
cold, recovery is found to be impossible. The power which exists in
these animals, however, of generating a large amount of heat within
their bodies, acts as a compensation for the want of the faculty pos-
sessed by the cold-blooded tribes ; since they can resist for a great
length of time (if in their healthy or normal condition) the depressing
influence of a temperature sufficiently low to produce a complete
suspension in the activity of the latter.

138. It only remains to say a few words regarding the degree of
heat w'hich certain Animals can sustain without prejudice, and which
even appears to be genial to them. Among the higher classes, this
range see?ns to be capable of great extension. Thus many instances
are on record of a heat of from 250° to 280° being endured, in dry
air, for a considerable length of time, without much inconvenience ;
and persons who have become habituated to this kind of exposure
can (with proper precautions) sustain a temperature of from 350° to
500°. In all such cases, however, the real heat of the body under-
goes very little elevation ; for, by means of the copious evaporation
from its surface, the external heat is prevented from acting upon it.
But if this evaporation be prevented, either by an insufficiency in the
supply of fluid from within, or by the saturation of the surrounding
air with moisture, the temperature of the body begins to rise ; and it
is then found, that it cannot undergo an elevation of more than a few
degrees, without fatal consequences. Thus in several experiments
which have been tried on different species of warm-blooded animals,
for the purpose of ascertaining the highest temperature to which the
body could be raised without the destruction of life, it was found that
as soon as the heat of the body had been increased, by continued
immersion in a limited quantity of hot air (which would soon become
charged with moisture), to from 9° — 13° above the natural standard,
the animals died. In general. Mammals die, when the temperature
of their bodies is raised to about 111°; the heat which is natural to
the bodies of Birds. The latter are killed by an equal amount of
elevation of bodily heat above their natural standard.

139. Hence we see that the actual range of temperature, within
which vital activity can be maintained in warm-blooded animals, is
extremely limited ; a temporary elevation of the bodily heat to 13°
above the natural standard, or a depression to 30° below it, being
positively inconsistent, not merely with the continuance of vital ope-
rations, but also with the preservation of vital properties ; and a con-
tinued departure from that standard, to the extent of only a very few
degrees above or below it, being very injurious. The provisions
■with which these animals are endowed, for generating heat in their
interior, so as to supply the external deficiency, and for generating
cold (so to speak), w^hen the external temperature is too high, are
therefore in no respect superfluous : but are positively necessary for
the maintenance of the life of such animals, in any climate, save one
whose mean should be conformable to their standard, and w^hose

OF HEAT AS A VITAL STIMULUS. 97

extremes should never vary more than a very few degrees above or
below it. Such a climate does not exist on the surface of the earth.

140. The range oi external temperature, within which cold-blooded
animals can sustain their activity, is much more limited, as well in*
regard to its highest as to its lowest point ; notwithstanding that the
range of bodily heat, which is consistent with the maintenance of their
life, is so much greater. In those which, like the Frog, have a soft
moist skin, which permits a copious evaporation from the surface, a
considerable amount of heat may be resisted, provided the air be dry,
and the supply of fluid from within be maintained.* But immersion
in w^ater of the temperature of 108°, is almost immediately fatal. In
many other cold-blooded animals, elevation of the temperature induces
a state of torpidity, analogous to that which is produced by its de-
pression. Thus the Helix pomatia (Edible Snail)' has been found to
become torpid and motionless in water at 112°; but to recover its
energy when placed in a colder situation. It would seem to be partly
from this cause, but partly also from the deprivation of moisture, that
the hottest part of the tropical year brings about a cessation of activity
in many tribes of cold-blooded animals, as complete as that which
takes place during the winter of temperate climates.

141. The highest limit of temperature compatible with the life of
Fishes has not been certainly ascertained : and it appears probable
that there are considerable variations in this respect amongst different
species. Thus it is certain that there are some which are killed by
immersion in water at 104°; whilst it is also certain that others can
not only exist, but can find a congenial habitation, in water of 113°,
or even of 120°; and examples of the existence of Fishes in thermal
springs of a much higher temperature than this, have been put on
record. Various fresh water Mollusca have been found in thermal
springs, the heat of w^hich is from 100° to 145°. Rotifera and other
animalcules have been met with in water at 112°. Larvae of Tipulee
have been found in hot springs of 205°; and small black beetles,
which died when placed in cold water, in the hot sulphur baths of
Albano. Entozoa inhabiting the bodies of Mammalia and of Birds
must of course be adapted to a constant temperature of from 98° to
110°; and they become torpid w^hen exposed to a cool atmosphere.
These lowly organized animals seem more capable of resisting the
effects of extreme heat, than any others; — at least if we are to credit
the statement, that the Entozoa inhabiting the intestines of the Carp
have been found alive, when the Fish was brought to table after
being boiled. — In all such cases, it is to be remembered, the heat of
the animal body must correspond with that of the fluid in which it is

* The Frog has a remarkable provision for this purpose ; in a bladder, which is
strudurally analogous to our Urinary bladder, but which has for its chief function to
contain a store of fluids for the exhaling process. It has been noticed that, when this
store is exhausted by continued exposure of the animal to a warm dry atmosphere, the
bladder becomes full again, when the animal is placed in a moist situation, even though
it take in no liquid by its mouth.

9^ OF ELECTRICITY AS A VITAL STIMULUS.

immersed ; and we have here, therefore, evident proof of the compati-
bility of vital activity, in certain cases, with a very elevated tempera-
ture. Additional and more exact observations, however, are much
wanting on this subject.

3. On Electricity y as a Condition of Vital Action.

142. Much less is certainly known with respect to the ordinary
influence of this agent, than in regard to either of the two preceding ;
and yet there can be little doubt, from the efiects we observe when it
is powerfully applied, as well as from our knowledge of its connection
Avith all Chemical phenomena, that it is in constant though impercep-
tible operation. Electricity differs from both Light and Heat in this
respect ; — that no -manifestation of it takes place so long as it is uni-
formly diffused, or is in a state of equilibrium; but in proportion as
this equilibrium is disturbed, by a change in the electric condition of
one body, which is prevented, by its partial or complete insulation,
from communicating itself to others, in that proportion is ^ force pro-
duced, which exerts itself in various ways according to its degree.
The mechanical effects of a powerful charge, when passed through a
substance that is a bad conductor of Electricity, are well known ; on
the other hand, the chemical effects of even the feeblest current are
equally obvious. The agency of Electricity in producing Chemical
change is the more powerful, in proportion as there is already a pre-
disposition to that change ; thus, as already remarked, the largest col-
lection of oxygen and hydrogen gases, or of hydrogen and chlorine,
mingled together, may be caused to unite by the minutest electric
spark, which gives the required stimulus to the mutual affinities that
were previously dormant. Hence it cannot but be inferred, that its
agency in the Chemical phenomena of living bodies must be of an
important character; but this may probably be exerted rather in the
way of aiding decomposition, than of producing new combinations,
to which (as we have seen) Light appears to be the most effectual
stimulus. Thus it has been shown that pieces of meat, that have
been electrified for some hours, pass much more rapidly into decom-
position, than similar pieces placed under the same circumstances,
but not electrified. And in like manner, the bodies of animals that
have been killed by electric shocks, have been observed to putrify
much more readily than those of similar animals killed by injury to
the brain. It is well known, moreover, that in thundery weather, in
which the electric state of the atmosphere is much disturbed, various
fluids containing organic compounds, such as milk, broth, &c., are
peculiarly disposed to turn sour ; and that saccharine fluids, such as
the wort of brewers, are extremely apt to pass into the acetous fer-
mentation.

143. The actual amount of influence, however, which Electricity
exerts over a growing Plant or Animal, can scarcely be estimated.
It would, perhaps, be the most correct to say, that the state of Elec-

i

GF ELECTRICITY AS A VITAL STIMULUS. 90

trie equilibrium is that which is generally most favourable ; and we
find that there is a provision in the structure of most living beings,
for maintaining such an equilibrium, — not only between the different
parts of their own bodies, but also between their own fabrics and the
surrounding medium. Thus a charge given to any part of a Plant or
Animal, is immediately diffused through its whole mass; and though
Organized bodies are not sufficiently good conductors to transmit very
powerful shocks without being themselves affected, yet a discharge
of any moderate quantity may be effected through them, without any
permanent injury, — and this more especially if it be made to take
place slowly. Now the points on the surfaces of Plants appear par-
ticularly adapted to effect this transmission ; thus it has been found
that a Leyden jar might be discharged by holding a blade of grass
near it, in one-third of the time required to produce the same effect
by means of a metallic point ; and an Electroscope furnished with
Vegetable points has been found to give more delicate indications of
the electric state of the atmosphere, than any other. Plants designed
for a rapid growth have generally a strong pubescence or downy
covering; and it does not seem improbable that one purpose of this
may be, to maintain that equilibrium between themselves and the
atmosphere, which would otherwise be disturbed by the various ope-
rations of vegetation, and especially by the process of evaporation,
which takes place with such activity from the surface of the leaves.

144. There appears to be sufficient evidence that, during a highly
electrical state of the atmosphere, the growth of the young shoots of
certain plants is increased in rapidity ; but it would be wrong thence
to infer that this excitement is useful to the process of Vegetation in
general, or that the same kind of electric excitement universally ope-
rates to the benefit or injury of the Plant. From some experiments
recently made it would appear, that potatoes, mustard and cress, cine-
rarias, fuchsias, and other plants, have their development, and, in
some instances, their productiveness, increased by being made to
grow between a copper and a zinc plate, connected by a conducting
wire ; while, on the other hand, geraniums and balsams are destroyed
by the same influence. The transmission of a series of moderate
sparks through plants, in like manner, has been found to accelerate
the growth of some, and to be evidently injurious to others. It is not
unreasonable to suppose, that, as a great variety of chemical processes
are constantly taking place in the growing plant, an electric disturb-
ance, which acts as a stimulus to some, may positively retard others;
and that its good or evil results may thus depend upon the balance
between these individual effects. This would seem the more likely
from the circumstance, that, in the process of Germination, the che-
mical changes concerned in which are of a simpler character, Elec-
tricity seems to have a more decided and uniform influence. The
conversion of the starch of the seed into sugar, which is an essential
part of this change, involves the liberation of a large quantity of car-
bonic, and of some acetic acid. Now as all acids are negative, and

IGO OF ELECTRICITY AS A VITAL STIMULUS.

as like electricities repel each other, it may be inferred that the seed
is at that time in an electro-negative condition ; and it is accordingly
found that the process of germination may be quickened, by connection
of the seed with the negative pole of a feeble galvanic apparatus,
whilst it is retarded by a similar connection with the positive pole.
A similar acceleration may be produced by the contact of feeble alka-
line solutions, which favour the liberation of the acids; whilst, on
the same principle, a very small admixture of acid in the fluid with
which the seed is moistened, is found to produce a decided retarda-
tion.

145. It is well known that Trees and Plants may be easily killed
by powerful electric shocks; and that, when the charge is strong
enough (as in the case of a stroke of lightning), violent mechanical
effects, — as the rending of trunks, or even the splitting and scattering
of minute fragments, — are produced by it. But it has also been
ascertained, that charges which produce no perceptible influence of
this kind, may destroy the life of Plants; though the effect is not
always immediate. In particular it has been noticed, that slips and
grafts are prevented from taking root and budding. There can be
little doubt that, in these instances, a change is effected in the chemi-
cal state of the solids or fluids ; although no structural alteration is
perceptible.

146. In regard to the influence of Electricity upon the Organic
functions of Animals, still less is certainly known ; but there is evi-
dence that it may act as a powerful stimulant in certain disordered
states of them. Thus in Amenorrhea, a series of slight but rapidly-
repeated electric shocks will often bring on the catamenial flow ; and
it is certain that chronic tumours have been dispersed, and dropsies
relieved by the excitement of the absorbent process, through similar
agency. Again, it is indubitable that a highly electric state of the
atmosphere produces very marked effects on the general state of many
individuals ; and brings on in some a degree of languor and depres-
sion, which cannot be accounted for in any other way. An instance
is on record, in which the atmosphere w^as in such an extraordinary
state of electric disturbance, that all pointed bodies within its influ-
ence exhibited a distinct luminosity ; and it was noticed, that all the
persons who were exposed to the agency of this highly electrified air,
experienced spasms in the limbs and an extreme state of lassitude,

147. Animals, like Plants, are liable to be killed by shocks of Elec-
tricity; even when these are not sufficiently powerful to occasion any
obvious physical change in their structure. But, as formerly men-
tioned (§ 69) there can be no doubt that minute changes may be
produced in their delicate parts, which are quite sufficient to account
for the destruction of their vitality, ev^en though these can only be
discerned with the Microscope. The production of changes in the
Chemical arrangement of their elements, is, however, a much more
palpable cause of death ; since it maybe fully anticipated beforehand,
and can easily be rendered evident. To take one instance only ; —

OF MOISTURE AS A VITAL STIMULUS, IQl

it is well known, that albumen is made to coagulate, i. e., is changed
from its soluble to its insoluble form, under the influence of an elec-
tric current; and it cannot be doubted that the production of this
change in the fluids of the living body (almost every one of which con-
tains albumen), even to a very limited extent, is quite a sufficient
cause of death, even in animals that are otherwise most tenacious of
life. " I once discharged a battery of considerable size," says Dr.
Hodgkin, " through a common Earth-worm, which would in all pro-
bability have shown signs of life long after minute division. Its
death was as sudden as the shock; and the semi-transparent sub-
stance of the animal was changed like Albumen which has been
exposed to heat.^'

148. Electricity possesses, in a remarkable degree, the power of
exciting the Contractility of Muscular fibre ; but this series of pheno-
mena will be more fitly described, when the properties of that tissue
are under consideration.

4. Of Moisture, as a Condition of Vital Action.

149. Independently of the utility of Water as an article of food,
and of the part it performs in the Chemical operations of the living
body, by supplying two of their most important materials (oxygen and
hydrogen), there can be no doubt that a certain supply of moisture is
requisite, as one of the conditions without which no vital actions can
go on. It has been already remarked, indeed, that one of the distin-
guishing peculiarities of organized structures, is the presence in all
of them of solid and fluid component parts ; and this in the minutest
portions of the organism, as well as in the aggregate mass. And in
all the vital, as well as in the chemical actions, to which these struc-
tures are subservient, the presence of fluid is essential. All nutrient
materials must be reduced to the fluid form, before they can be assimi-
lated by the solids ; and, again, the solid matters which are destined
to be carried ofi' by excretion, must be again reduced to the liquid
state, before they can be thus withdrawn from the body. The tissues
in which the most active changes of a purely vital character are per-
formed,— namely, the Nervous and Muscular, — naturally contain a
very large proportion of water; the former as much as 80, and the
latter 77, per cent. On. the other hand, in tissues whose function is
of a purely mechanical nature, such as Bone, the amount of fluid is
as small as is consistent with the maintenance of a certain amount of
nutrient action in its interior. By the long-continued application of
dry heat to a dead body, its weight was found to be reduced from
120 pounds to no more than 12 ; so that, taking the average of the
whole, the amount of water, not chemically combined, but simply
interstitial, might be reckoned at as much as 90 per cent. It is cer-
tain, however, that much decomposition and loss of solid matter must
have taken place in this procedure ; and we shall probably estimate
the proportion more accurately, if we regard the weight of the fluids

102 OF MOISTURE AS A VITAL STIMULUS.

of the human body as exceeding that of the solids by six or seven
times.

150. There is a great variation in this respect, however, among
different tribes of living beings. There are probably no highly-
organized Animals, v^^hose texture contains less fluid than that of Ver-
tebrata (unless, it may be, certain Beetles); but there can be no ques-
tion that, among some of the Zoophytes, the proportion of solids to
fluids is just the other way. In those massive coral-forming animals,
which, seem to have been expressly created for the purpose of build-
ing up islands and even continents from the depths of the ocean, we
find the soft tissues confined to the surface, and all within of a rocky
hardness. It is not, however, correct to say (as is commonly done),
that the coral-polypes build up these stony structures as habitations
for themselves; for the stony matter is deposited, by an act of nutri-
tion, in the living tissue of these animals, just as much as it is in the
bones of Man. But the parts once consolidated henceforth remain
dead, so far as the animal is concerned ; they are not connected with
the living tissues by any vessels, nerves, &c.; their density prevents
them from undergoing any but a very slow disintegrating change, so
that they require and receive no nutrient materials ; and they might
be altogether removed, by accident or decay, without any direct in-
jury to the still active, because yet unconsolidated, portions of the
polype-structure.

151. There is a close correspondence, in this respect, between the
condition of the stony or horny stem of a Coral, and the heart-wood of
the trunk of a Tree ; for the latter, becoming consolidated by internal
deposit, for the purpose of affording mechanical support, is thence-
forth totally unconnected with the vegetative operations of the tree,
and might be removed (as it frequently is by natural decay) without
affecting them. In all the parts, in which the nutrient processes are
actively going on, do we observe that the tissue contains a large pro-
portion of water ; and that, if the succulent portions be dried up,
their vital properties are destroyed. Thus it is in the soft tissue at
the extremities of the radicles or root fibres, that the function of
absorption takes place with the greatest activity; so that these parts
have received the name of spongioles: it is in the cells which form
the soft parenchyma of the leaves, that the elaboration of the sap
takes place, the fixation of carbon from the atmosphere, and the pre-
paration of the peculiar secretions of the plant: and it is in the space
between the bark and the wood, which is occupied (at the season of
most active growth) by a saccharine glutinous fluid, that the formation
of the new layers of wood and bark takes place. Now, as soon as
these parts become consolidated, they cease to perform any active
vital operations. The spongioles, by the lengthening of the root-
fibres, become converted into a portion of those fibres, and remain
subservient merely to the transmission of the fluids absorbed ; the
leaves gradually become choked by the saline and earthy particles
contained in the ascending sap, which they have had no power of

OF MOISTURE AS A VITAL STIMULUS. 103

excreting, and they wither, die, and fall off; and the new layers of
wood and bark, when once formed, undergo but little further change,
and are subservient to little else than the transmission of the ascend-
ing and descending sap to the parts where they are to be respectively
appropriated.

152. There are some remarkable instances in both the Animal and
Vegetable kingdoms, of an immense preponderance in the amount of
the fluids over that of the solids of the structure. This is character-
istic of the whole class of Jicalephce or Jelly-Fish^ giving to their
tissues that softness from which their common name is derived ; these
animals, in consequence, are unable to live out of water; for, when
they are removed from it, a drain of their fluids commences, which
soon reduces their weight to a degree that destroys their lives, — a
Medusa weighing fifty pounds being thus dried down to a weight of
as many grains. The most remarkable instances of a parallel kind
among Plants, are to be found in the tribe of Fungi ; certain mem-
bers of which are distinguished by an almost equally small proportion
of solid materials in their textures, presenting a most delicate gossa-
mer-like appearance to the eye, and possessing such little durability,
that they come to maturity and undergo decay in the course of a few
hours. These are not inhabitants of the water, but will vegetate only
in a very damp atmosphere.

153. As we find various Plants and Animals very differently con-
structed in regard to the amount of fluid contained in their tissues, so
do we also find them dependent in very different degrees upon a con-
stant supply of external moisture. There is no relation, however,
between the succulence of a plant, and the degree of its dependence
upon water; in fact, we commonly find the most succulent plants
growing in the driest situations; whilst the plants, which are adapted
to localities where they can obtain a constant supply of fluid, are not
usually remarkable for the amount of water in their own structure.
This, however, is easily explained. We find the most succulent
plants, — such as the Sedums or Stone-crops of our own country, and
the Cacti and Euphorbice of the tropics, — in dry exposed situations,
where they seem as if they would be utterly destitute of nutriment.
The fact is, however, that they lose their fluid by exhalation very
slowly, in consequence of their small number of stomata ; whilst, on
the other hand, they absorb with great readiness during rainy weather,
and are enabled, by the fleshiness of their substance, to store up a
large quantity of moisture until it is required. In some parts of
Mexico, the heat is so intense, and the soil and atmosphere so dry,
during a large part of the year, that no vegetation is found at certain
seasons, save a species of Cactus ; this affords a wholesome and
refreshing article of food, on which travelers have been able to
subsist for many days together, and without which these tracts would
form impassable barriers. On the other hand, the plants of damp
situations usually exhale moisture almost as fast as they imbibe it ;
and consequently, if their usual supply be cut off or diminished, they

104 OF MOISTURE AS A VITAL STIMULUS.

soon wither and die. Plants that usually live entirely submerged,
are destitute of the cuticle or thin skin, which covers the surface in
other cases ; in consequence of this, they very rapidly lose their fluid,
when they are removed from the water ; and they are hence depend-
ent upon constant immersion in it for the continuance of their lives,
although their tissues may not be remarkable for the amount of fluid
which they contain.

154. There are some Plants which are capable of adapting them-
selves to a great variety of situations, differing widely as to the
amount of moisture which their inhabitants can derive from the soil
and atmosphere ; and we may generally notice a marked difference
in the mode of growth, when we compare individuals that have
grown under opposite circumstances. Thus a plant from a dry
exposed situation, shall be stunted and hairy, whilst another, of the
same species, but developed in a damp sheltered situation, shall be
rank and glabrous (smooth). But in general there is a certain quan-
tity of moisture congenial to each species ; and the excess or deficiency
of this condition has, in consequence, as great an influence in deter-
mining the geographical distribution of Plants, as the amount of light
and heat. Thus, as already remarked, the Orchidese and Tree Ferns
of the tropics grow best in an atmosphere loaded with dampness ;
whilst the Cactus tribe, for the most part, flourishes best in dry
situations. The former become stunted and inactive, if limited in
their supply of aerial moisture ; whilst the latter, if too copiously
nourished, become dropsical and liable to rot. Among the plants of
our own country, we find a similar limitation ; a moist boggy situation
being indispensable to the growth of some, whilst a dry exposed
elevation is equally essential to the healthy development of others.
There is a beautiful species of exotic Fern, the Trichomanes sped-
osum ; the rearing of which has been frequently attempted in this
country and elsewhere, without success ; but which only requires an
atmosphere saturated with dampness, for its healthy development,
being easily reared in one of Mr. Ward's closed glass cases. In this,
as in similar examples, it is only necessary to imitate as closely as
possible the conditions under which the species naturally grows ; and
sometimes this can only be accomplished, by surrounding the plant with
small trees and shrubs, so as to give it a moister atmosphere than it
could otherwise attain. Professor Royle mentions the growth, under
such circumstances, of a fine specimen of the Xanthochymus dulcis,
one of the Guttiferce or Gamboge-trees, in the garden of the King of
Delhi ; this tree is naturally found only in the southern parts of India;
and the success of its cultivation in this northerly situation is entirely
due to its being sheltered by the numerous buildings within the lofty
palace wall, surrounded by almost a forest of trees, and receiving the
benefit of perpetual irrigation from a branch of the canal which flows
through the garden.

155. In regard to the influence of external moisture upon Animal
life, there is much less to be said ; since the mode in which fluid is

OF MOISTURE AS A VITAL STIMULUS. 105

received into the system is so entirely different. It may be remark-
ed, however, that Animals habitually living beneath the water, like
submerged Plants, are usually incapable of sustaining life for any
length of time when removed from it, in consequence of the rapid
loss of fluid which they undergo from their surface. It is, however,
by the desiccation of the respiratory surface, preventing the due aera-
tion of the blood, that the fatal result is for the most part occasioned;
since we find that when there is a special provision to prevent this,
as in the case of certain Fishes and Crustacea, the animals can quit
the water for a great length of time. There can be no doubt that the
amount of Atmospheric moisture is one of those conditions, which
are collectively termed Climate, and which influence the geographical
distribution of Animals, no less Ihan that of Plants. But it is difficult
to say how far the variations in moisture act alone. There can be
no doubt, however, of their operation ; for every one is conscious
of the effect, upon his health and spirits, of such variations as take
place in the climate he may inhabit. The two principal modes in
which these will operate, will be by accelerating or checking the
exhalation of fluid from the skin and from the pulmonary surface ;
for when the air is already loaded with dampness, the exhaled mois-
ture cannot be carried off with the same readiness as w^hen it is in a
condition of greater dryness ; and it will consequently either remain
within the system, or it will accumulate and form sensible perspira-
tion.

156. Now each of these states may be salutary, being the one best
adapted to particular constitutions, or to different states of the same
individual. A cold drying wind shall be felt as invigorating to the
relaxed frame, as it is chilling to one that has no warmth or moisture
to spare ; on the other hand, a warm damp atmosphere, which is
refreshing to the latter, shall be most depressing to the former. All
who have tried the effect of closely-fitting garments, impervious to
moisture, are well aware how oppressive they soon become ; this feel-
ing being dependent upon the obstruction they occasion to the act
of perspiration, by causing the included air to be speedily saturated
with moisture. When the fluids of the system have been diminished
in amount, either by the suspension of a due supply of water, or by
an increase in the excretions, there is a peculiar refreshment in a
soft damp atmosphere, or in a warm bath, w^hich allows the loss to
be replaced by absorption through the general cutaneous surface.
The reality of such absorption has been placed beyond all doubt,
by observations upon men, who had been exposed to a hot dry air
for some time, and afterwards placed in a warm bath ; for it was
found that the system would by this unusual means supply the
deficiency, which had been created by the previous increase in the
transpiration.

157. The effect of a moist or dry atmosphere, then, upon the Ani-
mal body, cannot be by any means unimportant ; although, as we
shall hereafter see, there exists in it a series of the most remarkable

106 OF MOISTURE AS A VITAL STIMULUS.

provisions for regulating the amount of its fluids. The influence of
atmospheric moisture, however, is most obvious in disordered states
of the system. Thus in persons who are subject to the form of
Dyspepsia called atonic, which is usually connected with a gene-
rally-relaxed condition of the system, a very perceptible influence is
experienced from changes in the quantity of atmospheric moisture ;
the digestive power, as well as the general functions of the body,
being invigorated by dryness, and depressed by damp. Again, there
is no doubt that, where a predisposition exists to the Tuberculous
Cachexia, it is greatly favoured by habitual exposure to a damp
atmosphere, especially when accompanied by cold ; indeed it would
appear, from the influence of cold damp situations upon animals
brought from warmer climates, that these two causes may induce the
disease, in individuals previously healthy. On the other hand, there
are some forms of pulmonary complaints, in which an irritable state
of the mucous membrane of the bronchial tubes has a large share ;
when this irritation presents itself in the dry form, a warm moist
atmosphere is found most soothing to it; whilst a drier and more
bracing air is much more beneficial, when the irritation is accom-
panied by a too copious secretion.

158. Although, as already stated, no vital actions can go on with-
out a reaction between the solids ^nd fluids of the body, yet there may
be an entire loss of the latter, in certain cases, without necessarily
destroying life; the structure being reduced to a state of dormant
vitality, in w^hich it may remain unchanged for an unlimited period ;
and yet being capable of renewing all its actions, when moisture is
again supplied. Of this we find numerous examples among both the
Vegetable and the Animal kingdoms. Thus the Mosses and Liver-
worts, which inhabit situations where they are liable to occasional
drought, do not suffer from being, to all appearance, completely dried
up; but revive and vegetate actively, as soon as they have been
thoroughly moistened. Instances are recorded, in which Mosses that
have been for many years dried up in a Herbarium, have been re-
stored by moisture to active life. There is a lycopodium (Club-Moss)
inhabiting Peru, which, when dried up for want of moisture, folds its
leaves and contracts into a ball ; and in this state, apparently quite
devoid of animation, it is blown hither and thither along the surface
by the wind. As soon, however, as it reaches a moist situation, it
sends down its roots into the soil, and unfolds to the atmosphere its
leaves, which, from a dingy brown, speedily change to the bright
green of active vegetation. The Anastatica (Rose of Jericho) is the
subject of similar transformations; contracting into a ball, when dried
up by the burning sun and parching air ; being detached by the wind
from the spot where its slender roots had fixed it, and rolled over the
plains to indefinite distances; and then, when exposed to moisture,
unfolding its leaves, and opening its rose-like flower, as if roused
from sleep. There is a blue Water- Lily, abounding in several of the
canals at Alexandria, which at certain seasons become so dry, that

OF MOISTURE AS A VITAL STIMULUS. 107

their beds are burnt as hard as bricks by the action of the sun, so as
to be fit for use as carriage roads ; yet the plants do not thereby lose
their vitality ; for when the water is again admitted, they resume their
growth with redoubled vigour.

159. Among the lower Animals, we find several of considerable
complexity of structure, which are able to sustain the most complete
desiccation. This is most remarkably the case in the common Wheel-
Animalcule; which may be reduced to a state of most complete dry-
ness, and kept in this condition for any length of time, and which will
yet revive immediately on being moistened. The same individuals
may be treated in this manner, over and over again. Experiments
have been carried still further with the allied tribe of Tardigrades ;
individuals of which have been kept in a vacuum for thirty days,
with sulphuric acid and Chloride of Calcium (thus suffering the most
complete desiccation the Chemist can effect), and yet have not lost
their vitality. It is singular that in this desiccated condition, they
may be heated to a temperature of 250°, without the destruction of
their vitality; although, when in full activity, they will not sustain a
temperature of more than from 112° to 115°. Some of the minute
Entomostracous Crustacea, which are nearly allied to the Rotifera,
appear to partake with them in this curious faculty. Many instances
are on record, in which Snails and other terrestrial Molhisca have
revived, after what appeared to be complete desiccation ; and the
eggs of the Slug, when dried up by the sun or by artificial heat, and
reduced to minute points only visible with the Microscope, are found
not to have lost their fertility, when they are moistened by a shower
of rain, or by immersion in water, which restores them to their former
plumpness. Even after being treated eight times in this manner, the
eggs were hatched when placed in favourable circumstances ; and
even eggs in which the embryo was distinctly formed, survived such
treatment without damage. That such capability should exist in the
animals and eggs just mentioned, shows a remarkable adaptation to
the circumstances in which they are destined to exist ; since were it
not for their power of surviving desiccation, the races of Wheel-
Animalcules and Entomostraca must speedily become extinct, through
the periodical drying-up of the small collections of water which they
inhabit ; and a season of prolonged drought must be equally fatal to
the terrestrial MoUusca.

160. It would seem that many cold-blooded animals are reduced,
by a moderate deficiency of fluid, to a state of torpidity closely resem-
bling that induced by cold ; and hence it is, that during the hottest
and driest part of the tropical year, there is almost as complete an
inactivity, as in the winter of temperate regions. The common Snail,
if put into a box without food, constructs a thin operculum or parti-
tion across the orifice of the shell, and attaches itself to the side of
the box: in this state it may remain dormant for years, without being
affected by any ordinary changes of temperature ; but it will speedily
revive if plunged in water. Even in their natural haunts, the ter-

108 OF MOISTURE AS A VITAL STIMULUS.

restrial Mollusca of our own climates are often found in this state
during the summer, when there is a continued drought; but with the
first shower they revive and move about. In like manner it is ob-
served that the rainy season, between the tropics, brings forth the
hosts of insects, which the drought had caused to remain inactive in
their hiding-places. Animals thus rendered torpid seem to have a
tendency to bury themselves in the ground, like those which are
driven to winter-quarters by cold. Mr. Darwin mentions that he
observed, with some surprise, at Rio de Janeiro, that, a few days
after some little depressions had been changed into pools of water
by the rain, they were peopled by numerous full-grown shells and
beetles.

161. This torpidity consequent upon drought is not confined to
Invertebrated animals. There are several Fish, inhabiting fresh
water, which bury themselves in the mud when their streams or pools
are dried up, and which remain there in a torpid condition until they
are again moistened. This is the case with the curious Lepidosiren,
which forms so remarkable a connecting link between Fishes and the
Batrachian Reptiles; it is an inhabitant of the upper parts of the
river Gambia, which are liable to be dried up during much more than
half the year; and the whole of this period is spent by it in a hollow
which it excavates for itself deep in the mud, where it lies coiled up
in a completely torpid condition, — whence it is called by the natives
the sleeping-fish. When the return of the rainy season causes the
streams to be again filled, so that the water finds its way down to the
hiding-place of the Lepidosiren, it comes forth again for its brief
period of activity; and with the approach of drought, it again works
its way down into the mud, which speedily hardens around it into a
solid mass. In the same manner, the Pi^oteus^ an inhabitant of certain
lakes in the Tyrol, which are liable to be periodically dried up, retires
at these periods to the underground passages that connect them, where
it is believed to remain in a torpid condition; and it thence emerges
into the lakes, as soon as they again become filled with water. The
Lizards and Serpents, too, of tropical climates, appear to be subject to
the same kind of torpidity, in consequence of drought, as that which
affects those of temperate regions during the cold of winter. Thus
Humboldt has related the strange accident of a hovel having been
built over a spot, where a young Crocodile lay buried, alive though
torpid, in the hardened mud; and he mentions that the Indians often
find enormous Boas in the same lethargic state ; and that these revive
when irritated or wetted with water. — All these examples show the
necessity of a fixed amount of fluid, in the animal structure, for the
maintenance of vital activity ; whilst they also demonstrate, that rtie
preservation of the v\\?i\ properties of that structure is not always in-
compatible with the partial, or even the complete, abstraction of that
fluid; the solid portions being then much less liable to decomposition
by heat, or by other agencies, than they are in their ordinary con-
dition.

ELEMENTARY PARTS OF ANIMAL STRUCTURES. 109

CHAPTER III.

OF THE ELEMENTARY PARTS OF ANIMAL STRUCTURES.

162. In the investigation of the operations of a complex piece of
Mechanism, and in the study of the forces which combine to produce
the general result, experience shows the advantage of first examining
the component parts of the Machine, — its springs, wheels, levers,
cords, pulleys, &c., — determining the properties of their materials,
and ascertaining their individual actions. When these have been
completely mastered, the attention may be directed to their combined
actions; and the bearing of these combinations upon each other, so
as to produce the general result, w^ould be the last object of study.

163. This seems the plan which the Student of Physiology may
most advantageously pursue, in the difficult task of making him'self
acquainted with the operations of the living fabric, and with the mode
in which they concur in the maintenance of Life. He should first
examine the properties of the component materials of the structure
in their simplest form ; these he will find in its nutrient fluids. He
may next proceed to the simplest forms of organized tissue, which
result from the mere solidification of those materials, and whose pro-
perties are chiefly of a mechanical nature. From these he will pass
to the consideration of the structure and vital actions of those tissues
that consist chiefly of cells; and will investigate the share they take
in the various operations of the economy. Next his attention will
be engaged by the tissues produced by the transformation of cells ;
of which some are destined chiefly for affording mechanical support
to the fabric, and others for peculiar vital operations. And he will
be then prepared to understand the part, which these elementary tis-
sues severally perform in the more complex organs. A due know-
ledge of these elementary parts, and of their physical, chemical, and
vital properties, is essential to every one who aims at a scientific
knowledge of Physiology. True it is, that we may study the results
of their operations, without acquaintance with them ; but we should
know^ nothing more of the worldng of the machine, than we should
know of a cotton-mill, into which we saw cotton-wool entering, and
from which we saw woven fabrics issuing forth ; or of a paper-mak-
ing-machine, which we saw fed at one end with rags, and discharg-
ing hot-pressed paper, cut into sheets, at the other. The study of
these results affords, of course, a very important part of the know-
ledge we have to acquire respecting the operations of the machine ;
but we could learn from them very little of the nativre of the separate
processes effected by it ; still less should we be prepared, by any dis-
order or irregularity in the general results, to seek for, and rectify,

110 ELEMENTARY PARTS OF ANIMAL STRUCTURES.

the cause of the disturbance in the working of the machine, by which
the abnormal result was occasioned.

164. Now just as in a Cotton-mill, there are machines of several
different kinds, adapted to effect different steps of the change, by
which the raw material is converted into the woven fabric, so do we
find that in the complex animal fabric there is a great variety of or-
gans for performing the several changes, by which the fabric itself is
built up and maintained in a condition fit for the performance of its
peculiar operations. These operations are the phenomena of sensa-
tion, of spontaneous motion, and of mental action. They are the
great objects of .y3?iimaZ existence ; just as the combination of ele-
ments into organic substances, that are to furnish the materials of the
Animal fabric, seems to be the great purpose of Vegetative Life. The
vital phenomena which are peculiar to Animals, are manifestations of
the properties of certain forms of organized matter, — the Nervous and
Muscular tissues, — which are restricted to themselves ; just as those
which are common to Animals and Plants, are effected by organized
structures, which are found alike in both kingdoms. Here, then, w^e
have the essential distinction between these kingdoms ; — namely the
presence in Animals of a peculiar apparatus, and the consequent
possession by them of peculiar endowments, which are totally wanting
in Plants. In the lowest forms of Animal life, we are obliged to infer
the presence of the characteristic structure, from the obvious exist-
ence of the peculiar endowments ; the minuteness of their entire fabric
being such, as to prevent the discovery of distinct muscular and
nervous fibres. But there are many species, indeed whole tribes, in
which it is impossible to say with certainty, how far sensibility and
spontaneity of action may be justly inferred from the movements they
exhibit ; and as other distinguishing characters are deficient, it is
undetermined (and perhaps will ever remain so) to which kingdom
they ought to be assigned.

165. All the operations, then, which are common to Animals and
Plants, are concerned in the building-up of the organized fabric, in
the maintenance of its integrity, and in the preparation of the germs
of new^ structures, to compensate for the loss of the parent by death.
These operations, as formerly explained (§ 44), involve a series of
very distinct processes ; which, although all performed by the simple
cell of the humblest plant, are distributed in more complex structures
through a number of parts or organs ; whose several actions are almost
as separate as those of the dissimilar machines of the cotton-mill, —
although, like them, sustained by the same powers, and so far mutu-
ally dependent, that neither of them can be suspended without in a
short time putting a stop to the rest. Now just as in each of the
machines of the cotton-mill we may have similar elements, — such as
wheels, levers, pulleys, bands, &c., — put together in different me-
thods, and consequently adapted for different purposes, as carding,
spinning, weaving, &c,, so shall we find in the animal body, that
these different organs are composed of very similar elements, and that

ELEMENTARY PARTS OF ANIMAL STRUCTURES. HI

the individual actions of these elementary parts are the same ; but that
the difference of result is the consequence of the variety in their
arrangement. Thus we shall find that the growth of cells, their ab-
sorption of certain matters from the surrounding fluids, and their sub-
sequent liberation of these by the bursting or liquefying of the cell-wall
Avhen their term of life is come to an end, are means employed in one
part of the body to introduce nutrient materials into the current of the
circulation, whilst in another the same processes are used as means
to withdraw, from that very same current, certain substances of which
it is necessary to get rid. Now certain combinations of elementary
structure, adapted to the performance of a set of actions tending to
one purpose, and thus resembling one of the machines of a cotton-
mill, is termed an organ; and the sum-total of its actions is termed its
function. Thus w^e have in the function of Respiration, which essen-
tially consists of an interchange of oxygen and carbonic acid between
the air and the blood, a multiiude of distinct changes, some of them
of a character apparently not in the least related to it, but all neces-
sary, in the higher and more complex fabric, to bring the blood and
the air into the necessary relation. The sum-total of these changes
constitutes the function of Respiration ; and the structures by which
they are effected are organs of Respiration.

166. The whole organized structure, then, may be regarded as
made up of distinct organs^ having their several and (to a certain ex-
tent) independent purposes ; and these organs may be resolved, in like
manner, into simple elementary parts, whose structure and composi-
tion are the same, in whatever part of the fabric they occur. And in
like manner, the phenomena of Life, considered as a whole, may be
arranged under several groups or functions, according to the imme-
diate purpose to which they are directed ; and yet in every one of
these groups, we shall find repeated the same elementary changes
which are concerned in the rest. Thus in the act of Respiration, the
same kind of muscular movements, the same sort of nervous agency,
are concerned, as contribute to the ingestion of the food ; and a simi-
lar circulation of the blood, to that which supplies the materials for
the nutrition of the tissues. Hence we see the propriety of applying
ourselves first to the consideration of the elementary parts of the living
structure, and of the properties by which they effect the changes,
that are characteristic of its several organs.

1. Of the original Components of the Animal Fabric.

167. As we can best study the original Components of the Animal
Fabric, by investigating their properties before the process of Organi-
zation begins, or whilst it is taking place, we must have recourse for
this purpose to the nutrient fluid, — the Blood, — in which these are
contained in the state most completely prepared for the reception of
the Vitalizing influence. The same substances may be found, in an
earlier stage of preparation, in the Chyle and Lymph ; and also in the

112 PROTEINE-COMPOUNDS.

Eggs of oviparous animals. The circumstances attending the develop-
ment of the latter afford, indeed, the most satisfactory proof of the
convertibility of the simple chemical product. Albumen, with certain
inorganic substances, into every form of organized structure. For the
white of the egg consists of nothing else than albumen, combined with
phosphate of lime ; whilst the yetk is chiefly composed of the same
substance, mingled with oily matter, and a minute quantity of sul-
phur, iron, and some other inorganic bodies. Yet this albumen and
fatty matter are converted by the germ, after the lapse of a few days,
under the simple stimulus of an elevated temperature, into a complex
fabric, composed of bones, muscles, nerves, tendons, ligaments, car-
tilages, fibrous membranes, fat, cellular tissue, &c. &c., and endowed
with the properties characteristic of all these substances, which, when
brought into consentaneous activity, manifest themselves in the Life
of the chick. In tracing these wonderful transformations, therefore,
we should rightly commence with Albumen. But as recent Chemical
researches have shown, that this may be considered as a compound
of the more simple substance termed Proteine, with Phosphorus and
Sulphur, and as its relations to the compounds formed in Vegetable
growth are thereby rendered more apparent, it will be desirable to
commence with the latter, which has been truly said to be the most
universally-present, and most important to life, of all the substances
known to the Organic Chemist.

168. Proteine may be detected in almost every part of the Vegeta-
ble as well as of the Animal fabric, in various conditions and states
of combination ; being found in a soluble form in their fluids, and in
an insoluble state in their solid parts. It may be obtained by dissolv-
ing boiled Albumen in a weak solution of caustic alkali; and by then
neutralizing the liquid by an acid, which causes its precipitation in
the form of grayish-white flocks. And it may also be obtained from
the Gluten of wheat flour (the substance which is left when dough is
washed with w^ater so as to separate the starch from it), by the very
same process. After being washed, it is gelatinous, of a grayish
colour, and semi-transparent ; when dried, it is yellowish, hard, easily
pulverized, tasteless, insoluble in water and alcohol, and decomposed
by heat- without fusing. There is no perceptible difference, either
in elementary composition, or in chemical relations with other sub-
stances, between the two specimens of Proteine thus obtained by the
same process from the Animal and Vegetable kingdoms. They are
both composed, according to Mulder, of 40 Carbon, 31 Hydrogen, 5
Nitrogen, and 12 Oxygen ;* they are rendered soluble by alkalies,
and are precipitated again by acids ; and they form with the latter and
with oxygen, definite chemical compounds, from which the combining
equivalent just stated is determined. Proteine unites also with Sul-

* The formula of Liebig is different ; being 48 Carbon, 36 Hydrogen, 6 Nitrogen,
14 Oxygen. That of Mulder agrees equally well with the proportions of the elements,
as deduced from analysis; and seems to represent more accurately the combining
equivalent of this substance.

PROTEINE-COMPOUNDS. 113

phur and Phosphorus, in various proportions ; and it is never found
free from these, or in a simple uncombined state.

169. The azotized substances obtained from Plants, which have
received the names of Vegetable Albumen^ Vegetable Fibrin, and
Vegetable Casein, are all compounds of proteine with the last-named
elements; but the exact amount of the latter has not been certainly
ascertained in each case ; the proportion they bear to the proteine
being so small, as to render the analysis difficult. These proteine-
compounds are found in the youngest parts of the roots of plants; and
are probably formed there, and transported by the circulation of the
sap into distant parts. The milk-white colour of certain vegetable
juices is partly due to the large quantity of these substances which
they contain. The deposition of the proteine-compounds in certain
groups of cells, in a solid condition, would be sufficiently accounted
for by the agency of an acid, which changes it from its soluble to its
insoluble form ; whilst, on the other hand, its removal from one set
of cells, and its transference to others, might be accomplished by an
alkaline solution, which would re-dissolve it. That such a transference
really does take place, appears from the fact, that the proportion of
the proteine-compounds contained in old cells is much less than that
of the young and growing parts; from which, therefore, it seems to
be removed at a subsequent time. The principal differences in the
properties of the three compounds above named are these. Vegetable
Albumen, and Legurain or Vegetable Casein, are both of them solu-
ble in cold water; but the former is coagulated by heat, and may be
obtained in this manner from the fresh saps of most plants ; whilst the
latter is not coagulated by heat, but may be precipitated by acids from
water in which the meal of peas or beans has been soaked. The
substance termed Vegetable Fibrin, or more correctly Coagulated
Vegetable Albumen, is insoluble in water ; and is the azotized matter
existing in the seeds of corn, in almonds, &c., which is not taken up
by water. Besides these, there is another termed glutin to be obtained
from wheat flour, by the agency of alcohol, in which it is soluble.

170. It is certain that the proteine-compounds of Plants are trans-
ferred into the bodies of Animals, and become, with little or no change,
the materials of their organizing processes. Whether similar com-
pounds may be formed within the animal body, at the expense of any
of the other materials supplied by plants, has not yet been certainly
ascertained ; but the preponderance of evidence appears on the nega
tive side. According to Mulder, the proportions in which Sulphur
and Phosphorus are united with Proteine, in the Animal body, are as
follows : — in the Albumen of blood-serum, 2 Sulphur, and 1 Phospho-
rus, to 10 Proteine; — in Fibrin and the Albumen of eggs, 1 Sulphur,
and 1 Phosphorus, to 10 Proteine; — in Casein, 1 Sulphur to 10 Pro-
teine;— and in the substance of which the Crystaline lens of the eye
is chiefly made up, 1 Sulphur to 10 Proteine. The small proportion
of the additional elements is no argument against their being of great
importance in the constitution of these bodies ; for Inorganic Chemistry

8

114 PROTEINE-COMPOUNDS.

furnishes numerous examples, in which the presence or absence of a
body that bears a very small proportion to the whole, makes a vast
difference in the properties of the compound. Thus Arseniuretted
Hydrogen, which is one of the most poisonous of all gases, contains
less than 2 per cent, of Hydrogen; yet it is to this small quantity, that
the peculiar character and gaseous state of this compound are owing.
Still more remarkable is the fact mentioned by Sir J. Herschel, that
by alloying mercury with a millionth of its weight of sodium, a power
of not less than 50,000 times that of gravity is instantaneously gene-
jated, when the alloy is submitted to galvanic influence. — It cannot
be doubted, however, from considerations presently to be stated, that
« far greater diflerence exists between animal Albumen and animal
Fibrin^ than between any of the corresponding principles in Plants ;
«nd that this difference is due much less to diversity in composition
(for according to Mulder, the amount of all the components is the
•same in the Fibrin of blood and in the Albumen of the egg), than to
« -change in the arrangement of the ultimate particles.

171. According to Mulder, Proteine unites with Oxygen in definite
proportions, so as to form a binoxide and a tritoxide. These are both
produced when Fibrin is boiled in water for some time ; the latter
being then found dissolved, whilst the former remains insoluble. The
tritoxide may also be formed by boiling Albumen for some time in
water, and is in like manner taken up in solution ; but the insoluble
residue is still albumen. It is further obtainable by decomposing the
chlorite of proteine with ammonia. In its properties it somewhat
resembles gelatin, and has been mistaken for that substance. There
is reason to think that this compound really exists as such in the
blood ; a small quantity of it being formed every time that the blood
passes through the lungs, and given out again when it returns to the
system ; and a much larger amount being generated during the in-
flammatory process, so that it may be easily obtained from the " buffy
coat" by boiling. It is also contained in pus, which is a product of
the inflammatory process. — The binoxide is quite insoluble in water,
but dissolves in dilute acids. It may be obtained by dissolving hair in
potash, adding a little acid to throw down the proteine, and then
adding a large excess of acid, which precipitates the binoxide. Ac-
cording to Mulder, this compound also is produced in small quantity
at every respiration; and it enters into the normal composition of
several of the animal tissues. These views, however, must still be
received with some hesitation.

172. One of the most characteristic and important properties of
Proteine, is the facility with which it undergoes decomposition, when
acted on by other chemical substances, especially by alkalies. If a
proteine-compound be brought into contact with an alkali, ammonia
is immediately disengaged ; indeed, the alkaline solution can hardly be
made weak enough to prevent the disengagement of ammonia. This
is a property, which must be continually acting in the living body ;
since the blood has a decided alkaline reaction. If either albumen,

PROTEINE-COMPOUNDS.— ALBUMEN. • 115

or any other proteine-compound, be boiled with potash, it is com-
pletely decomposed ; — not, however, being resolved at once into its
ultimate constituents, or altogether into simple combinations of them,
but in great part into three other organic compounds, Leucin, Protid,
and Erythroprotid. — Leucin is a crystaline substance, which forms
colourless scales, destitute of taste and odour ; it is soluble in water
and alcohol, and sublimes unchanged. It consists of 12 Carbon, 12
Hydrogen, 1 Nitrogen, and 4 Oxygen. There is not at present any
evidence that it is produced in the living body; and the chief interest
which attaches to it arises from the fact, that it may^be procured from
Gelatin as well as from Proteine ; which indicates a near relationship
between these two substances. — The two other compounds, Protid
and Erythroprotid^ are uncrystaline substances, the former of a straw-
yellow, and the latter of a reddish-brown colour ; they belong to the
class of bodies which was formerly included under the vague general
term of extractive matter; and both in their chemical composition,
and their solubility in water, they bear a strong resemblance to Gela-
tin. The first of them consists of 13 C, 9 H, 1 N, 4 O ; and the
second of 13 C, 8 H, 1 N, 5 0 ; whilst the formula of Gelatin is 13
C, 10 H, 2 N, 5 O. — Besides these substances, Ammonia, with Formic
and Carbonic Acids, are produced ; the acids unite w^ith the potash,
employed to effect the decomposition ; and the ammonia is set free.

173. We have next to speak of that one of the proteine-compounds
in the living body, which corresponds most closely with those yielded
by Plants, and which serves as the material at the expense of which
all the rest may be formed, by chemical transformations analogous to
the preceding. This is Mbumen ; which exists in solution in the
Blood and Chyle ; and which makes up the largest part of the yelk,
and the whole of the white, of the Egg. In its soluble state, it is
always combined with a small quantity of free soda, with which it
seems to be united as an acid with its base ; and to this state of com-
bination, its solubility is regarded by most Chemists as being due.
When the fluid in w^hich it is dissolved is evaporated at a low tem-
perature (not exceeding 126°), the Albumen, or rather Albuminate of
Soda, maybe dried, without losing its solubility ; when dried, it may
be exposed to a temperature of 212°, without undergoing change ;
and it forms, when again dissolved in water, the same glairy, colour-
less, and nearly tasteless fluid as before. When a higher temperature
is employed, however, the Albumen passes into the insoluble form ;
and presents itself either as a cloudy or flocculent precipitate, or as a
firm consistent coagulum, according to the strength of the original
solution. The same condition regulates the amount of heat requisite
for the purpose ; thus if the quantity of albumen be so great that the
liquid has a slimy aspect, a temperature of 145° or 150° is suflScient
for the purpose, and the whole becomes solid, white, and opaque ;
but in a very dilute condition, boiling is required, and the albumen
then separates in the form of white finely-divided flocks. In either
case, the soda, and other soluble salts are separated from the albumen.

116 ' ALBUMEN; CASEIN.

and remain dissolved in the water. When the coagulation of Albu-
men takes place rapidly, the coherent mass seems quite homogeneous,
and shows no trace of anything like definite arrangement ; hut when
the process is more gradual, minute granules present themselves,
which do not, however, exhibit a tendency towards any higher form
of structure. The insoluble coagulum, or pure Albumen, dries up to
a yellow, transparent, horny substance ; which, when macerated in
water, resumes its former whiteness and opacity. — Pure Albumen
may also be obtained from the solid mass, which remains when an^
Albuminous fluid is dried at a low temperature, by reducing it to a
fine powder, and then washing it with cold water on a filter ; common
salt, with sulphate, phosphate and carbonate of soda, is dissolved
out ; and a soft swollen mass remains upon the filter, which has all
the characters of Albumen, obtained by precipitation, except that it is
readily soluble in a solution of nitrate of potash, which will not dis-
solve the latter substance.

174. Albumen may also be thrown down from its solution, in a
coagulated state, by Alcohol, Creasote, and by most Acids, when
these are added in excess, so as to do more than neutralize the alkali.
Nitric acid is particularly eflBcacious in occasioning coagulation ; on
the other hand. Acetic acid, and common or tribasic Phosphoric acid
do not precipitate it, these acids having the property of dissolving
pure Albumen. In the precipitation of Albumen by an Acid, definite
compounds are formed between the two ; in which the Albumen acts
the part of a base. On the other hand, as already remarked, it serves
.as an acid in its combinations with the caustic Alkalies, and is held
in solution by them. Most of the metallic salts, as those of copper,
lead, mercury, &c., form insoluble compounds with albumen, and
thus give precipitates with its solution ; hence the value of white of
egg as an antidote, in cases of poisoning with corrosive sublimate.
The best method of detecting the presence of soluble albumen in
very small quantity, is to boil the liquid, and add nitric acid; if tur-
bidity is then produced, the existence of albumen may be inferred.

175. The existence of unoxidized Sulphur in Albumen, is shown
by the familiar fact of the blackening of a silver spoon by a boiled
egg; which is due to the formation of an alkaline Sulphuret during
the coagulation. A very important property of soluble Albumen is
its power of uniting with Phosphate of Lime, and rendering it solu-
ble; it is in this way, that the consolidating material of bones is
introduced into the body. About two per cent, of this salt may be
separated from Albumen in its coagulated state.

176. Nearly allied to Albumen is the substance termed Casein,
which replaces it in Milk; and this is worthy of notice here, because
it is the sole form in which the young Mammal receives Proteine into
its body, during the period of lactation. Like Albumen, this sub-
stance may exist in two forms, the soluble, and the insoluble or
coagulated ; and it further agrees with it, in requiring, as a condition
of its solubility, the presence of a free alkali, of which, however, a

ALBUMEN; CASEIN; FIBRIN. 117

very small quantity suffices for the purpose. It differs from Albumen,
however, in this ; that it does not coagulate by heat, and that it is
precipitated from its solution by Acetic acid. Casein is further re-
markable for the facility with which its coagulation is effected by the
contact of certain animal membranes, as in the ordinary process of
cheese-making. This change is considered by some Chemists to be
due, however, not to any direct action of the membrane upon the
casein, but to its influence in converting some of the milk-sugar into
lactic acid, which, separating the alkali of the casein, will occasion
the precipitation of the latter. The only difference w^hich can be
detected between Albumen and Casein, in regard to the proportions
of their elements, consists in the absence of Phosphorus in the latter;
but this can scarcely be the cause of the foregoing differences in their
properties. Casein appears to surpass Albumen in its power of com-
bining with the phosphates of lime and magnesia, and rendering them
soluble.

177. Albumen and Casein, then, may be regarded as constituting
the raw materials, at the expense of which the organized tissues of
the Animal fabric are built up ; and w^e have sufficient evidence, in
the development of the Chick from the egg, and of the young Mam-
mal from milk, that they may be transformed into any of the proteine
compounds which are to be found in the Animal body. How far they
may require to be united with fatty matter in producing some of these,
— as the Nervous, — can scarcely be yet determined ; but it is a cir-
cumstance worthy of note, that in both the foregoing cases, fatty mat-
ter is mingled with the albumen, in the aliment destined for the
development of the young animal. The purpose of this, however,
may be nothing else than the production of the Adipose tissue, and
the maintenance of the respiration. — Further evidence that Albumen
is the raw material of the Animal tissues, is derived from this; — that
it is the form to which all the proteine-compounds contained in the
food, whether derived from the Animal or from the Vegetable king-
dom, are reduced by the Digestive process; and in which, therefore,
they must be first received within the living system.

178. We find, however, in the fluids that are formed at the ex-
pense of this Albumen in the living body, namely the Chyle and the
Blood, another substance ; which is so closely related to Albumen in
its ultimate Chemical composition, as not to be distinguishable from
it with any degree of certainty; but w^hich yet differs from it in some
of its chemical properties, and still more in the tendency w^hich it ex-
hibits to assume the organized form and to manifest vital properties.
This substance is named Fibrin* \i is found in the Chyle or crude
blood, soon after it is drawn from the food ; it presents itself in gradu-

* According to the analyses of Dumas, there is a slight difference between Fibrin
and Albumen in ultimate composition; the former having less Carbon, aad more
Azote than the latter. The difference, however, is so trifling, that it may be doubted
whether the Analytical process is yet sufficiently certain and definite to substan-
tiate it.

118 FIBRIN.

ally-increasing proportion, as the Chyle slowly passes along the
Lacteal vessels, and through the Mesenteric glands, towards the ter-
mination of the Absorbent system in the Venous ; and it is also found
in the fluid contents of that other division of the Absorbent system,
the Lymphatics, which is distributed through the body at large, and
Avhich seems to have for its chief office to take up, and to re-introduce
into the circulating current, such particles contained in the fluids of
the tissues, as do not require to be at once cast out of the body, but
may be again employed in the process of Nutrition. But it is found,
above all, in the Blood, — the fluid whose ceaseless and rapid course
through the body supplies to every element of the structure the mate-
rials of its growth and development : and the varying proportions in
which it presents itself there, are evidently closely connected with
the formative powers of that fluid. It is also a principal element of
certain colourless exudations^ which are poured forth from wounded
or inflamed surfaces, or which are deposited in the interstices of in-
flamed tissues; these exudations, when possessed of a high formative
property (that is, a readiness to produce an organized tissue), are
said to be composed of coagulable or organizable lymph, which is
nothing more than the fibrinous element of the blood, in an unusually
concentrated state. We shall first notice the Chemical properties of
Fibrin ; and shall then inquire into those, which present the first
dawnings or indications of Vitality.

179. Like the other Proteine-compounds, Fibrin may exist in solu-
tion, or in an insoluble form ; but there is this important difference, —
that its soluble form is not a permanent one, and cannot be maintained
in any fibrinous fluid that has been drawn from the living vessels,
without the influence of re-agents, w^hich totally destroy its peculiar
properties. All investigations of a Chemical nature, therefore, must be
made upon insoluble Fibrin; and this may be obtained in its purest
state, by whipping fresh blood with a bundle of twigs, by w^hich opera-
tion, it will i3e caused, in coagulating, to adhere to the twigs, in the
form of long, white, elastic filaments, with scarcely an admixture of
foreign matter. When dried in vacuo, or at a gentle heat, it becomes
translucent and horny; and in this condition, it closely resembles
coagulated albumen. It further resembles that substance, in being
soluble in very dilute caustic alkali, and in phosphoric acid ; and the
solutions exhibit many of the properties of the similar solutions of
albumen. When the fibrin of venous blood is triturated in a mortar
with a solution of nitrate of potash, and the mixture is left for twenty-
four hours or more at a temperature of from 100° to 120°, it becomes
gelatinous, slimy, and eventually entirely liquid. In this condition, it
exhibits all the properties of a solution of Albumen which has been
neutralized by acetic acid. It coagulates by heat ; it is precipitated by
alcohol, corrosive sublimate, &c.; and, when largely diluted, it deposits
a flocculent substance, not to be distinguished from insoluble albumen.
The close Chemical relation of Fibrin and Albumen is further proved
by the ready conversion of the former into the latter in the act of di-

FIBRIN; ITS COAGULATION. 119

gestion; Animal flesh, which consists of Fibrin, being reduced to the
form of Albumen with the same facility as the Vegetable compounds,
which resemble the latter much more closely in the first instance. The
Fibrin of arterial blood, however, cannot be reduced to the fluid form
by solution with nitre ; and this appears to be due to the oxidized
condition of its Proteine; for in a solution of Venous fibrin in nitre,,
contained in a deep cylindrical jar, and having its surface freely ex-
posed to the air, a fine flocculent precipitate is gradually seen to form;
and this, when collected, is found to have the properties of arterial
fibrin. The Fibrin of Animal flesh agrees with that of venous, rather
than with that of arterial blood. Fibrin, like Albumen, unites with
acids as a base, forming definite compounds; and with bases as an
acid. It also possesses the property of uniting with the earthy phos-
phates; of which from '7 to 2*5 per cent, are found in the ash that is
left after its combustion.

180. We see, then, that when considered in its simply-Chemical
relations. Fibrin does not differ in any essential particular from Albu-
men ; and that the chief point of obvious variation, is the spontaneous
coagulation of the former, when it is removed from the living body.
There is, however, in the structure of the coagulum itself, a most im-
portant difference ; for instead of consisting of a homogeneous struc-
tureless mass, or of a simple aggregation of minute granules, it is found
by the Microscope, to possess a definite ^6roM5 arrangement, the fibres
crossing one another in every direction. In the ordinary coagulum or
clot of Blood, these fibres do not present any great degree of firmness :
they may be hardened, however, by boiling; and their arrangement
then becomes more definite. They may be seen much more clearly,
however, in the *' huffy coat" of Inflammatory blood ; in which there
is not only an increased proportion of Fibrin, but the Fibrin itself
seems to have undergone a higher elaboration, — that is, to have pro-
ceeded still further in the change towards regular organization. In
this state, the process of coagulation is unusually slow ; the clot formed
by the fibrous tissue is much more solid ; and it continues for some
hours, or even days, to increase in solidity, by the mutual attraction
of the particles composing the fibres, which causes them to contract
and to expel the fluid contained in their interstices.

181. The most perfect fibrous structure originating in the simple
coagulation of fibrin is to be found, however, in those exudations
which take place either from inflammation, or from a peculiar forma-
tive action, destined to repair an old tissue or to produce a new one.
Thus in Fig. 2 is shown the fibrous structure of a false membrane formed
by the consolidation of a fibrinous exudation from the surface of an
inflamed peritoneum. And in Fig. 3 is displayed a similar fibrous
structure (in which, however, the fibres have more of a reticulated
arrangement), which incloses the fluid contents of the egg, and enters
into the composition of the shell itself. As the ovum (which, at the
time of its quitting the ovarium, consists of the yelk-bag only) passes
along the oviduct of the parent, it receives its coating of albuminous

120

FIBRILLATION OF FIBRIN.

matter, of which layer after layer is thrown out by the vessels of the
oviduct. When a sufficient supply has thus been furnished, it appears

Fig. 2.

Fig. 3.

Fibrous structure of inflammatory exudation
from peritoneum.

Fibrous membrane, lining the egg-shell,
and forming the animal basis of the shell
itself.

that fibrinous instead of albuminous matter is poured forth ; and this,
in coagulating, forms a very thin layer of fibrous tissue, which en-
velops the albumen. Layer after layer is gradually added ; and at
last, by the superposition of these layers, that firm tenacious mem-
brane is formed, which is afterwards found lining the egg-shell. The
process is then continued, with this variation, that carbonate of lime
is also secreted from the blood in a chalky state ; and its particles lie
in the interstices of the fibrous network, and give it that solidity which
is characteristic of the shell. If they be removed by the agency of a
weak acid, or if the bird be not sufficiently supplied w^ith lime at the
time of laying, the outer membrane has the same consistence as the
inner ; and either may be separated, after prolonged maceration, by
dextrous manipulation, into a series of layers of a fibrovis matting
like that represented in Fig. 3.

182. It is scarcely possible to deny to such a tissue the designation
of an organized structure, even though it contains no vessels, and
may not participate in any further Vital phenomena. We shall here-
after find, that a tissue presenting very similar characters forms a
large part of the Animal fabric ; and that the vessels with which it is
copiously supplied, have for their object nothing else than the remo-
val of its disintegrated or decaying portions, and the deposition of new
matter in a similar form (§ 194). In the production of new parts,
w^e find this simple fibrous tissue performing the important function of
serving as a matrix or bed for the support of the vessels ; and as, by
the more gradual transformation of the nutritive materials they bring,
new and more permanent tissues are formed, the original one gradu-
ally undergoes disintegration, and all traces of it are in time lost. This
would appear to be the history of the Chorion of the Mammalian
ovum ; which is at first nothing else than a fibrous unvascular bag,
formed round the ovum in its passage through the Fallopian tube,

FIBRILLATION OF FIBRIN. 121

precisely after the manner of the shell-membrane of the Bird's egg;
but which is afterwards penetrated by vessels proceeding from the
embryo, and in time acquires a new structure (Chap. XI.)

183. The completeness of the production of such a fibrous tissue
depends in part, as we have seen, upon the degree of elaboration
which the Fibrin has undergone ; but in great part also upon the
nature of the surface, on which the coagulation takes place. Thus
we never find so perfect a membrane formed by the consolidation of
the Fibrin out of the living body, — on a slip of glass for example, —
as when it takes place on the surface of a living membrane, or in the
interstices of a living tissue. This may perhaps be accounted for by
the fact, that the coagulation takes place much more slowly in the
latter case than in the former ; and that the particles may thus have
more time to arrange themselves in the definite fibrillation^ which
seems to be their characteristic mode of aggregation : — ^just as crys-
talization takes place best when the action is slow ; and as a substance,
whose particles would remain in an amorphous or disunited form if
too rapidly precipitated from a solution, may present a most regular
arrangement when they are separated from it more slowly. Of this
view it would seem to be a confirmation, that the most perfect fibril-
lation out of the body is usually seen in those cases, in which coagu-
lation takes place least rapidly.

184. The conditions under which the spontaneous coagulation of
Fibrin takes place, are best known from the observation of that pro-
cess as it occurs in the Blood; and although this fluid, as we shall
hereafter see, is of a very complex nature, yet as the Fibrin alone is
concerned in its coagulation, and as that act appears to take place in
the same manner as if no other substance was present, there appears to
be no objection to the employment of the phenomena of Blood-coagu-
lation as the basis of our account of the properties of Fibrin. — There
can be no doubt, from Microscopical observation of the circulating
Blood, that Fibrin is in a state of perfect solution in the fluid ; and
in this condition it remains, so long as it is in motion in the living
body. That its fluidity, however, does not depend only upon its
movement, is evident from two facts; — first, that no kind of motion
seems effectual in preventing the coagulation of the blood, after it has
been drawn from the vessels; — and second, that a state of rest within
the living body does not immediately produce coagulation ; a portion
of blood, included between two ligatures in a living vessel, remain-
ing fluid for a long time. On the other hand, it seems certain that
the state of vitality of the parts with which the blood is in contact,
has a great influence in preserving its fluidity ; thus it has been found
that, if the Brain and Spinal Cord of an animal be broken down, and
by this measure the vitality of the body at large be lowered, clots of
blood are formed in their trunks within a few minutes. Nevertheless,
a mass of blood effused into a cavity of the living body, undergoes
coagulation almost as soon as it would in a dead vessel; but this may
be accounted for by the very small surface which is in contact with

122 COAGULATION OF FIBRIN.

the blood, as compared with the mass of the latter. It must be re-
membered that the circulating blood is continually being subdivided
into countless streams ; and that each of these passes through the
living tissue, in such a manner that all its particles are in close rela-
tion with the living surface. Moreover it is probable that the form
of matter which we term Fibrin never remains long in that condi-
tion, in the ordinary state of the system ; being continually withdrawn
by the nutritive processes, and as continually reformed from the Al-
bumen, by an elaborating action hereafter to be considered. Hence
we may regard the state of motion through living vessels, as essen-
tial to the permanent continuance of fibrin in the fluid form.

185. The length of time, however, during which Fibrin may re-
main uncoagulated, after it has been withdrawn from the living body,
varies according to various conditions ; some of which are not well
understood. In the first place, as already remarked, the more ela-
borated and more concentrated the condition of the Fibrin, the more
slowly does it usually coagulate. Thus when a large quantity of
blood is drawn at one bleeding, into several vessels, that w^hich
flows first takes the longest time to coagulate, and forms the firmest
clot ; whilst that which is last drawn coagulates most rapidly and
with the least tenacity. The coagulation is accelerated by moderate
heat, and retarded by cold; but it is not prevented even by extreme
cold ; for if blood be frozen immediately that it is drawn, it will coa-
gulate on being thawed, — thus preserving its vitality, in spite of the
freezing process, like the organized structures of many of the lower
animals. Again, the coagulation is accelerated by exposure to air ;
but it is not prevented, though it is retarded, by complete exclusion
from it. Various Chemical agents retard the coagulation, without
preventing it ; this is the case especially with solutions of the neutral
salts. The coagulation is not so firm, however, or the fibrillation so
perfect, after the use of these ; and there can be no doubt that they
modify the properties of the fibrin by acting chemically upon it.

186. After remaining in this condition for a certain length of time,
the Fibrin undergoes a further change, which is evidently the result
of decomposition ; the coagulum becomes soft, and exhibits appear-
ances of putrefaction. This takes place the more rapidly, as the first
coagulation was less complete. Thus in the imperfectly-elaborated
Fibrin of the Chyle, the coagulum is sometimes so incomplete that
it does not separate itself from the serum, and liquefies again in half
an hour. In certain states of disease, the solidifying properties of the
Fibrin are very much impaired ; so that it soon liquefies and decom-
poses. In these cases, there is scarcely any trace of the characteristic
fibrous arrangement of the particles. — On the other hand, the fibrin-
ous coagulum of inflamed blood, as it is more solid, is also more per-
sistent, than that of ordinary blood ; and the greatest persistency of
all is seen in the fibrous network formed by exudation, as in the cases
just now mentioned.

187. The coagulating power of Fibrin, — in other words, its pecu-

SIMPLE FIBROUS TISSUES. 123

liar vital property, — may be destroyed by various causes operating
within the living body; so that the blood remains fluid after death.
These may be classed under three heads. In the first place, the
vitality of the fibrin may be destroyed by substances introduced into
the blood from without; which have the power of acting in the man-
ner of ferments^ and which occasion an obvious chemical change in
its condition. This is the case in the severe forms of Typhoid fever,
which are termed malignant ; and especially those which result from
the contact of putrescent matter, as Glanders, Pustule maligne, &c.
Secondly, it may be impaired or altogether destroyed by morbid ac-
tions originating in the system itself, and depending upon irregular
nutrition or imperfect excretion ; thus the blood has been found fluid
after death, in severe cases of Scurvy and Purpura, also in cases of
Asphyxia (consequent upon the retention of carbonic acid in the
blood), and in the bodies of over-driven animals. The same result
may follow, Thirdly, from violent shocks or impressions, which sud-
denly destroy the vitality of the whole system at once; these maybe
such as are obviously capable of producing a chemical or mechanical
change, as in the case of death by Lightning or by a violent Electrical
discharge; or they may act through the nervous system, in a manner
not yet clearly understood, as when death results from concussion of
the brain, from a blow upon the epigastrium, from violent mental
emotion, or from a coup de soleil. — It is not to be supposed that the
non-coagulability of the Blood is a phenomenon by any means invari-
able under the foregoing circumstances ; but it has been occasionally
observed in all of them. We must not mistake, for the absence of
coagulating power, the remarkable retardation of the act of coagula-
tion which sometimes occurs. Thus, the blood is occasionally found
in a fluid condition in the bodies of persons that have been dead for
some days; and yet when withdrawn from the vessels it coagulates.
An instance has been lately put on record, in which blood drawn
from a patient suffering under an attack of pneumonia, did not coagu-
late for fifteen days, but then formed a firm clot, and was a month
before it putrefied.

2. Of the Simple Fibrous Tissues.

188. A large part of the Animal fabric, especially among the higher
classes in which the parts have the greatest amount of motion upon
one another, is composed of tissues, which seem as if they consisted
of nothing else than fibres, of the simple character already described,
woven together in various ways, according to the purposes they are
destined to serve. These fibres are altogether different from those
hereafter to be described as constituting the Muscular and Nervous
tissues, and must not be confounded with them. The former are solid,
and possess none but physical properties ; the latter are tubular, and
are distinguished by their peculiar vital endowments, which seem
chiefly, if not entirely, to reside in the contents of the tubular fibre.

124

SIMPLE FIBROUS TISSUES.

Fig. 4.

Simple fibrous tissue ; a
tissue ; 6, tendinous fibres.

fibres of areolar

The simple fibrous tissues, of which we have now to treat, appear to

have for their sole office in the
animal body to bind together the
other elementary parts into one
whole, without uniting them so
closely as to render them immov-
able; and we find the same elements
arranged in very different modes,
according to the purposes they are
destined to fulfil. Thus in the TeTi-
dons^ by which the Muscles are con-
nected with the Bones and impart
motion to them, the only property
required is that of resisting strain
or tension in one direction ; and in
these we find the fibres disposed in a parallel arrangement, passing
continuously in straight lines between the points of attachment. In
the Ligaments which connect the bones together, and which also have
for their purpose to afford resistance to strain, but which are liable to
tension in a greater variety of directions, we find bundles of fibres
crossing each other according to these directions ; and in some in-
stances we find the ligaments endowed also with a certain degree of
elasticity. The structure of the strong Fibrous Membranes^ which
form the envelops to different organs and bind together the contained
parts, is very similar ; each of these membranes being composed of
several layers of a dense network, formed by the interweaving of
bundles of fibres in different directions. In the Fibro- Cartilages, we
find a mixture of the characteristic structure of Ligament with that of
Cartilage ; bundles of fibres, similar to those which constitute the
former, being disposed among the cells which are the chief organized
constituents of the latter. In certain Fibro-Cartilages, however, these
fibres are endowed with a high degree of elasticity.

189. These two qualities, — that of resistance to tension without any
yielding, — and that of resistance combined with elasticity, — are cha-
racteristic of two distinct forms of Fibrous tissue, the Wliite and the
Yellow. The White Fibrous tissue presents itself under various forms ;
being sometimes composed of fibres so minute as to be scarcely dis-
tinguishable ; and sometimes presenting itself under the aspect of
bands, usually of a flattened form, and attaining the breadth of
l-500th of an inch. These bands are marked by numerous longitu-
dinal streaks, but they cannot be torn up into minute fibres of deter-
minate size ; hence they must be regarded as made up of an aggrega-
tion of the same elements as those which may become developed into
separate fibres. The fibres and bands are occasionally somewhat
wavy in their direction. This tissue, which is perfectly inelastic, is
easily distinguished from the other by the effect of Acetic acid, which
swells it up and renders it transparent, at the same time bringing into
view certain oval corpuscles, which are supposed to be the nuclei of

SIMPLE FIBROUS TISSUES.

125

the cells that were concerned in the formation of the tissue. — The
Yelloto Fibrous tissue exists in the form of long, single, elastic, branched

Fig. 5.

Fig. 6.

Fasciculus of fibres of white fibrous tissue
from lateral ligament of kiiee-jaijit.

Yellow fibrous tissue from ligamentum,
nuchae ; a, the fibres drawn apart, to show
their reticulate arrangement; b, the fibres in
situ.

filaments, with a dark decided border; which are disposed to curl
when not put on the stretch. They are for the most part between
l-5000th and l-10,000th of an inch in diameter; but they are often
met with both larger and smaller. They frequently anastomose, so as
to form a network, as shown in Fig. 6. This tissue does not undergo
any change, when heated with acetic acid. It exists alone (that is,
without any mixture of the white), in parts which require a peculiar
elasticity, such as the middle coat of the Arteries, the Chordae Vocales,
the Ligamentum Nuchae (of Quadrupeds), and the Ligamenta sub-
flava ; it enters largely into the composition of certain parts, which
are commonly regarded as Cartilaginous, such as the external ear;
and it is also a principal component of other tissues to be presently
described.

190. These tissues are very different in Chemical composition.
Those which are composed of the White fibrous element, — namely,
Tendons, Ligaments, &c. — are almost entirely resolved by long boil-
ing into the substance termed Gelatin or Glue ; and this is also
largely obtained from the skin, and from Mucous and Serous Mem-
branes, into which, as we shall presently see, that element enters
largely. The composition of Gelatin is much simpler than that of
the Protein-compounds ; so far, at least, as regards the number of
atoms of its several elements ; for it consists (according to Mulder)
of 13 Carbon, 10 Hydrogen, 2 Nitrogen, 5 Oxygen. This compo-
sition is the same, whether the Gelatin be obtained from isinglass,
from fibrous membranes, or from bones. The distinctive characters
of Gelatin are its solubility in warm water, its coagulation on cooling
into a uniform jelly, and its formation of a peculiar insoluble com-
pound with Tannic acid. Gelatin is very sparingly soluble in cold
water; though prolonged contact with it will cause the Gelatin to swell

126 SIMPLE FIBROUS TISSUES.

up and soften. Its power of forming a jelly on cooling is such, that a
solution of one part in 100 of water will become a consistent solid.
And its reaction with Tannic acid is so distinct, that the presence of
one part of Gelatin in 5000 of water is at once detected by infusion
of Galls. — There can be no doubt that Gelatin does not exist ex-
actly as such in the Fibrous tissues ; since none can be dissolved out
of them by the continued action of cold water, and it usually re-
quires the prolonged action of hot water, to occasion their complete
conversion. There are some substances, however, in which this is
not requisite; and from which the gelatin may be more readily ex-
tracted. This is the case, for example, with the air-bladder of the
Cod and other fish ; which, when cut into shreds and dried, is known
as Isinglass. It is the case also with the substance of bones, from
which the calcareous matter has been removed. In both instances
it would seem that the state of organization is very imperfect; scarcely
any traces of the fibrous structure being perceptible. When the
fibrous arrangement is more complete, the solubility of the tissue is
much diminished. Hence it would seem that the particles have a
different arrangement in the tissues, from that w^hich they have in the
product obtained by boiling. Their ultimate composition, however,
is the same ; for w^hen any serous membrane, or other tissue princi-
pally composed of the w^hite fibrous element, is analyzed by combus-
tion, the elements are found to have the same proportion to each
other as in Gelatin, allowance being made for the small admixture
of other substances. The action of Tannic acid, too, is the same on
the organized tissue, as it is on the gelatin extracted from it ; and
hence results its utility in producing an insoluble compound, not
liable to undergo decomposition, in the substance of the skin, con-
verting it into leather.

191. It is not yet known how Gelatin is produced in the Animal
body. There can be no doubt that it may be elaborated from Albu-
men ; since we find a very large amount of Gelatin in the tissues of
young animals, which are entirely formed from albuminous matter;
and also in the tissues of herbivorous animals, which cannot receive it
in their food, as Plants yield no substance resembling gelatin. It
has been suggested by Mulder, that Gelatin may be formed by the
decomposition of Protein, which has been already mentioned as taking
place from the agency of weak Alkaline solutions, (§ 172,) and which
must probably, therefore, be continually occurring in the blood.
For if to each atom of Protid and Erythroprotid, we add one of the
atoms of Ammonia, which are given off in that decomposition, we
have compounds, of which the former differs from Gelatin only by
the presence of two additional atoms of hydrogen and the deficiency of
one of oxygen, whilst the only difference in the latter consists in the
presence of one additional atom of hydrogen. Thus the ammoniated
erythroprotid, when exposed to oxygenation in the lungs, may have
its one superfluous atom of hydrogen carried off in the form of water,
and will then have the composition of Gelatin ; and the same result

SIMPLE FIBROUS TISSUES. 127

will be obtained from the ammoniated protid, by the addition of three
atoms of oxygen, which will convert it into gelatin and two atoms
of water. These transformations must be regarded for the present as
altogether theoretical; but it does not appear at all unlikely that they
may really take place.

192. The composition of the Yellow fibrous tissue appears to be
altogether dissimilar. It scarcely undergoes any change by prolonged
boiling; it is unaffected also by the weaker acids; and it preserves its
elasticity, if kept moist, for an almost unlimited period. According
to Scherer it consists of 48 Carbon, 38 Hydrogen, 6 Nitrogen, and 16
Oxygen ; and he considers it to be composed of an atom of Proteine
with two atoms of water. (See § 168, note.)

193. The simple Fibrous tissues appear to be very little susceptible
of change in the living body; and we find them very sparingly
supplied with blood-vessels. In the solid Tendons, the bundles of
straight parallel fibres are a little separated from each other by the
intervention of the Areolar tissue to be presently noticed ; and this
permits the sparing access of vessels to their interior. In the Fibrous
Membranes and Ligaments, this is found in somewhat larger amount;
and the vascularity of these tissues is rather greater.

194. The great use of the foregoing Tissues appears to be, to aflford
a firm resistance to tension; by which they may either communicate
motion, as in the case of Tendons ; or restrain it, as in the case of
Ligaments ; or altogether prevent it, as in the case of Aponeuroses
and Fibrous Membranes. With this firm resistance, a considerable
amount of elasticity may be combined. But we have now^ to notice a
tissue, in which a very different arrangement of the same elements
presents itself; and the object of this is, to bind together the elements
of the different fabrics of the body, and at the same time to endow
them with a greater or less degree of freedom of movement upon
one another. This tissue, which is called the Areolar, consists of a
network of minute fibres and bands, which are interwoven in every
direction, so as to leave innumerable areola or little spaces, which
communicate freely with one another. Of these fibres, some are of
the yellow or elastic kind ; but the majority are composed of the
white fibrous tissue, and, as in that form of elementary structure, they
frequently present the form of broad flattened bands, or membranous
shreds, in which no distinct fibrous arrangement is visible. The
interstices are filled during life with a fluid, which resembles very
dilute serum of the blood, consisting chiefly of water, but containing
a sensible quantity of common salt and albumen. This tissue, —
which has been frequently but erroneously termed Cellular, — is very
extensible in all directions, and very elastic, from the structural
arrangement of its elements. It cannot be said to possess any dis-
tinctly vital endowments ; for although it has a certain amount of
sensibility, this merely depends upon the presence of nerves which it
is conveying to other parts ; and the small amount of contractility

128 AREOLAR TISSUES.

which it shows, depends rather upon the muscular tissue of the ves-
sels that traverse it.

195. As already mentioned, we find this tissue in almost every
part of the body ; thus it binds together the ultimate fibres of the
Muscles into minute fasciculi, unites these fasciculi into larger ones,
these again into larger ones which are obvious to the eye, and these
into the entire muscle. Again it forms the membranous septa between
distinct muscles, or between muscles and fibrous aponeuroses. In like
manner it unites the elements of nerves, glands, &c. ; binds together
the fat-cells into minute bags, these into larger ones, and so on ; and
in this manner penetrates and forms a considerable part of all the softer
tissues of the body. But it is a great mistake to assert, as it wais
formerly common to do, that it penetrates the harder organs, such as
bones, teeth, cartilage, &c. Its purpose obviously is, to allow a cer-
tain degree of movement of the parts which it unites ; and hence we
find it entering much more largely into the composition of the Mam-
mary gland (which, from its attachment to the great pectoral muscle,
must have its parts capable of being shifted upon one another), than
into that of the Liver, Kidneys, &c. It also serves as the bed, in
which blood-vessels, nerves, and lymphatics may be carried into the
substance of the different organs ; and it often undergoes a degree of
condensation, in order to form a sheath for the larger trunks, which
gives it almost the characters of a Fibrous Membrane.

196. The quantity of fluid in the insterstices of Areolar tissue is
subject to considerable variations; but these depend rather upon the
state of fullness or emptiness of the vessels which traverse it, and upon
the condition of the walls of those vessels, than upon any change in
the tissue itself. It has been shown that, when an albuminous fluid
is in contact with an animal membrane, the watery part of the fluid
will pass through by transudation ; but that the albuminous matter
will be for the most part kept back, so that only a very small propor-
tion of it is to be found in the transuded liquid. This appears to be
a sufficient explanation of the presence of a weak serous fluid in the
cavities of areolar tissue ; and there is not any necessity, therefore, to
imagine the existence of a secreting power, either in the areolar tissue
itself, or in the walls of the capillaries which traverse it. When
there is a want of firmness or tone in the walls of the vessels, pro-
ducing (as we shall hereafter see, § 609) an increased pressure of the
contained fluid on their walls, and diminished resistance, the watery
part of the blood will have an unusual tendency to transudation ; and
we accordingly find that it then distends the areolse, and produces
dropsy. The physical arrangement of the parts of the tissue is so
much altered, that its elasticity is impaired ; and it consequently pits
on pressure, — that is, when pressure has made an indentation in the
surface, this is not immediately filled up when the pressure is with-
drawn, but a pit remains for some seconds or even minutes. The
free communication which exists amongst the interstices, is shown by
the influence of gravity upon the seat of the dropsical effusion; this

SEROUS MEMBRANES.— SKIN, AND MUCOUS MEMBRANES. 129

always having the greatest tendency to manifest itself in the most
depending parts, — a result, however, which is also due to the in-
creased delay, w^hich takes place in the circulation in such parts,
when the vessels are deficient in tone. This freedom of communica-
tion is still more shown, however, by the fact, that either air or water
may be made to pass, by a moderate continued pressure, into almost
every part of the body containing Areolar tissue; although introduced
at only a single point. In this manner it is the habit of butchers to
inflate veal ; and impostors have thus blown-up the scalps and faces
of»their children, in order to excite commiseration. The whole body
has been thus distended with air by emphysema in the lung; the air
having escaped from the air-cells into the surrounding areolar tissue,
and thence, by continuity of this tissue with that of the body in gene-
ral at the root or apex of the lungs, into the entire fabric.

197. The structure of the Serous and Synovial Membranes is
essentially the same with that of Areolar tissue. Their free surface
is covered with a layer of cells ; but these constitute a distinct tissue,
the Epitheliuniy of which an account will be given hereafter. The
epithelium lies upon a continuous sheet of membrane, of extreme deli-
cacy, in which no definite structure can be discovered ; the nature of
this, which is called the basement or primary-membrane, will be pre-
sently considered (§ 206). Beneath this is a layer of condensed
Areolar tissue, which constitutes the chief thickness of the serous
membrane, and confers upon it its strength and elasticity ; this gradu-
ally passes into that laxer variety, by which the membrane is attached
to the parts it lines, and which is commonly knowm as the sub-serous
tissue. The yellow fibrous element enters largely into the composi-
tion of the membrane itself; and its filaments interlace in a beautiful
network, which confers upon it equal elasticity in every direction.
The membrane is traversed by blood-vessels, nerves, and lymphatics,
in varying proportions ; some of the synovial membranes, especially
that of the knee-joint, are furnished with little fringe-like projections,
which are extremely vascular, and which seem especially concerned
in the secretion of the synovial fluid. The fluid of the serous cavities
is so nearly the same as the serum of the blood, that the simple act
of transudation is sufficient to account for its presence in their sacs; on
the other hand, that of the Synovial capsules, and of the Bursae Mu-
cosae which resemble them, may be considered as serum with from 6
to 8 per cent, of additional albumen.

198. The elements of Areolar tissue enter largely also into two
other textures, which perform a most important share in both the
Organic and the Animal functions ; — namely, the Mucous Membranes
and the Skin. These textures are continuous with each other; and
may, in fact, be considered as one and the same, modified in its dif-
ferent parts according to the function it is destined to perform. Thus
it is everywhere extremely vascular ; but the supply of blood in the
skin is chiefly destined for the nervous system, and is necessary to
the act of sensation ; whilst that of the internal skin or mucous mem-

9

130 SKIN, AND MUCOUS MEMBRANES.

brane is rather subservient to the processes of absorption and secre-
tion. This tissue is continued from the external surface of the body
by the several orifices and outlets of its cavities ; and it is further
continued most extensively from its primary internal prolongations,
into the inmost recesses of the glandular structures.

199. Thus the gastro-intestinal mucous membrane commences at
the mouth, and lines the whole alimentary canal from the mouth to
the anus, where it again becomes continuous wath the skin ; and it
sends off as branches, the membranous linings of the ducts of the sali-
vary glands, pancreas, and liver ; these membranes proceed into all
the subdivisions of the ducts, and line the ultimate follicles or ccEca
in which they terminate. Again the bronchia-pulmonary mucous
membrane commences at the nose, and passes along the air-passages,
down the trachea, through the bronchi and their subdivisions, to line
the ultimate air-cells of the lungs ; communicating in its course with
the gastro-intestinal. Another mucous membrane of small extent
commences at the puncta lachrymalia, lines the lachrymal sac and the
nasal duct, and becomes continuous with the preceding. Another,
w^hich may be considered a kind of offset from either of the first two,
passes up from the pharynx along the Eustachian tube, and lines the
cavity of the tympanum.

200. Near the opposite termination of the alimentary canal, more-
over, we have the genito-urinary mucous membranes ; these com-
mence in the male by a single external orifice, that of the urethra ; —
passing backwards along the urethra, the genital division is given off,
to line the seminal ducts, the vesiculse seminales, the vasa deferentia,
and the secreting tubuli of the testis ; another division proceeds along
the ducts of the prostate gland, to line its ultimate follicles, and an-
other along the ducts of Cowper's glands ; whilst the miliary division
lines the bladder, passes up along the ureters to the kidney, and then
becomes continuous with the membrane of the tubuli uriniferi. In
the female, the urinary division commences at once from the vulva ;
whilst the genital passes along the vagina into the uterus, and thence
along the Fallopian tubes to their fimbriated extremities, where it be-
comes continuous with the serous lining of the abdominal cavity, the
peritoneum.

201. Besides the glandular prolongations here enumerated, there
are many others, both from the internal and external surface. Thus
we have the Mammary mucous membrane, commencing from the
orifices of the lactiferous ducts, passing inwards to line their subdi-
visions, and forming the walls of the ultimate follicles. In the same
manner the Lachrymal mucous membrane is prolonged from the con-
junctival mucous membrane, w^hich covers the eye and lines the eye-
lids, and w^hich is continuous with the skin at their edges. There
are several minute glands, again, in the substance of the skin, and in
the walls of the alimentary canal, which need not be here enume-
rated; but which contribute immensely to the extension of the sur-
face of the raucous membrane ; a prolongation of this being the essen-

SKIN, AND MUCOUS MEMBRANES. 131

tial constituent in every one. In their simplest form, these glandulae
are nothing more than little pits or depressions of the surface ; these
are found both in the Skin and Mucous membrane, and are particularly
destined for the production of their protective secretions, hereafter to
be described.

202. We have seen, then, that the essential character of the Mu-
cous membranes, as regards their arrangement, is altogether different
from that of the serous and synovial membranes. For whilst the
latter form shut sacs, the contents of which are destined to undergo
little change, the former constitute the walls of tubes or cavities, in
which constant change is taking place, and which have free outward
communications. Thus in the gastro-intestinal mucous membrane,
we have an inlet for the reception of the food and a cavity for its
solution, the walls of which are endowed in a remarkable degree with
absorbing power, whilst they are also furnished with numerous glan-
dulae, which pour the solvent fluid into the cavity. On the other
hand, it has an outlet, through which the indigestible residuum is
cast forth, together with the excretions from the various glands that
pour their products into the alimentary tube. In the bronchio-pul-
monary apparatus, the same outlet serves for the introduction and for
the expulsion of the air; and here, too, is continual change. In other
cases, there is but a single outlet ; and the change is of a simpler cha-
racter, consisting merely in the expulsion of the matters eliminated
from the blood by the agency of the glands. Now it is, as we shall
see hereafter, in the digestion and absorption of food, on the one
hand, and in the rejection of effete matters on the other, that the
commencement and termination of the nutrient processes consist; and
these operations are performed by the system of Mucous-membranes,
including in that general term the Skin, which is an important organ
of excretion, besides serving as the medium through which sensory
impressions of a. general character are received by the Nervous system.

203. The Mucous Membrane may be said, like the serous, to con-
sist of three chief parts ; — the epithelium or epidermis covering its
free surface ; — the subjacent basement-membrane ; — and the areolar
tissue, with its vessels, nerves, &c., which forms the thickness of the
membrane, and connects it with the subjacent parts. The Epidermis
and Epithelium alike consist of cells ; but the function of the former
(which consists of several layers, of which the outer are dry and horny)
is simply protection to the delicate organs beneath ; whilst that of the
latter is essentially connected with the process of Secretion, as w^ill
be shown hereafter. The basement-membrane resembles that of the
serous membranes ; but its separate existence is unusually evident in
some parts where it exists alone, as in the tubuli uriniferi of the kid-
ney ; whilst it can with difficulty be demonstrated in others, as the
skin. The Areolar tissue of Mucous membranes usually makes up
the grea4:est part of their thickness ; and it is so distinct from that of
the layers beneath, constituting the sub-mucous tissue, as to be readily
separable from them. It differs not in any important particular, how-

132

SKIN, AND MUCOUS MEMBRANES.

ever, from the same tissue elsewhere ; and the white and fibrous
elements may be detected in it in varying proportions, in different
parts, — the latter being especially abundant in the skin and lungs,
which owe to it their peculiar elasticity. Hence the Mucous mem-
branes yield Gelatin in abundance, on being boiled. The skin also
appears to contain some of the non-striated Muscular fibre (§ 337),
in varying proportions in its different parts.

204. The relative amount of Blood-vessels, Nerves and Lympha-
tics, as already mentioned, is subject to great variation, according to

Fig. 8.

Distribution of Capillaries at the
surface of the skin of the finger.

Distribution of Capillaries in the
Villi of the Intestine.

the part of the system examined. The first, however, are most con-
stantly abundant, being required in the Skin for sensation, and in the
Mucous membranes for absorption and secretion. In fact we might
say of many of the mucous membranes, especially those of the glands,
that their whole purpose is to give support to the secreting cells, and
to convey blood-vessels into their immediate neighbourhood, whence
these cells may obtain materials for their development. The Skin is
the only part of the whole system which is largely supplied with

Fig. 9.

Fig. 10.

Distribution of Capillaries around
follicles of Mucous Membrane.

Distribution of Capillaries around the
follicles of Parotid Gland.

Nerves, except the Conjunctival membrane, and the Mucous mem-
brane of the nose ; hence the sensibility of the internal mucous mem-
brane is usually low, although its importance in the organic functions
is so great. The Skin is copiously supplied with Lymphatics ; and
the first part of the alimentary canal with Lacteals ; some of the
glandular organs are also largely supplied with Lymphatics.

BASEMENT OR PRIMARY MEMBRANE.

Fig. 11.

133

Distribution of the tactile nerves at the extremity of the human thumb, as seen in a thin perpendicu-
lar section of the skin,

205. The Areolar tissue, whether existing separately, or as forming
a part of the Serous and Mucous Membranes, is capable of being very
quickly and completely regenerated ; indeed, we often find that losses
of substance in other tissues are replaced by means of it. As to the
precise mode of its production, there is not yet a general agreement
amongst Microscopists ; some holding that its fibres are produced by the
transformation of cells in the manner hereafter to be described (§ 258
and Fig. 33); whilst others regard it as originating in the simple con-
solidation of Fibrin under peculiar circumstances. To the latter of
these opinions the Author inclines ; chiefly on account of the strong
resemblance between the fibres of Areolar tissue, and those which
are unquestionably formed by such a consolidation. It is not to be
denied, however, that traces of cells are to be met with amongst these
tissues; but as it will be shown that most, if not all, fibrinous exuda-
tions contain cells, their presence affords no proof that the mass of
fibres have originated in a process of transformation ; — the fact that a
definite fibrous tissue may have its origin in the coagulation of fibrin,
being beyond a doubt.

3. Of the Basement or Primary Membrane.

206. In many parts of the Animal body, w^e meet with membranous
expansions of extreme delicacy and transparency, in which no definite
structure can be discovered ; and these seem, like the simple fibres
already described, to have been formed, rather directly from the nu-
tritive fluid, than indirectly by any previous process of transformation.
Hence we may regard such membranes and fibres as constituting the
most simple or elementary forms of Animal tissue. The characters
of membranes of this kind were first pointed out by Mr. Bowman
and Mr. J. Goodsir ; by the former of whom it was termed basement-
membrane, as being the foundation or resting-place for the epithelium-
cells which cover its free surface (§ 231); w^hilst by the latter it was
termed the primary membrane, as furnishing the germs of those cells.
These terms appear equally appropriate, and may be used indiffer-
ently.— In its very simplest form, the basement-membrane is a pellicle
of such extreme delicacy, that its thickness scarcely admits of being

134 BASEMENT OR PRIMARY MEMBRANE.

measured ; it is, to all appearance, perfectly homogeneous, and pre-
sents not the slightest trace of structure under the highest powers of
the microscope, appearing like a thin film of coagulated gelatin.
Examples of this kind may be easily procured, by acting upon the
inner layer of any bivalve shell with dilute acid ; this dissolves away
the calcareous matter and leaves the basement-membrane. In other
cases, however, the membrane is not so ho-
^'s'^^- mogeneous; a number of minute granules

being scattered, with more or less of uni-
formity, through the transparent substance.
And w^e not unfrequently find, in place of
these uniformly distributed granules, a series
of distinct spots, arranged at equal or varia-
ble distances, and in different directions, as
shown in Fig. 12. Moreover, the mem-
Portion of the primary mem- braue thus coustitutcd is disDoscd to break

brane of Ihe human intra-glaud- . . _ , . ^ ^ n •> • \

ular lymphatics, with its germi- Up lUtO portlOUS Of equal SlZC, Cach 01 WhlCh

SlseToV^Jit""''^""' ""'"' contains one of these spots; whilst in the
more homogeneous forms previously de-
scribed, we find no such tendency, no appearance of any definite
arrangement being perceptible when they are torn. — Hence it would
seem as if the first and simplest form were produced by the simple
consolidation of a thin layer of homogeneous fluid ; the second, by a
layer of such fluid, including granules; and the third, by the coa-
lescence of flattened cells, whose further development had been
checked. — We find the primary membrane under one or other of
these forms, on all the free surfaces of the body, beneath the epithe-
lial or epidermic cells. Thus, as already mentioned, it constitutes the
outer layer of the true Skin ; it lines all the cavities formed by Mucous
membranes, and is prolonged into all the ducts and ultimate follicles
and tubuli of the Glands which are connected with them (§ 198); in-
deed it may be said in many instances to be the sole constituent of the
walls of these follicles and tubuli, the subjacent tissue not being con-
tinued to their finest ramifications. Again, it forms the innermost
layer of the serous and synovial membranes ; and it also lines the
blood-vessels and lymphatics, forming the sole constituent of the
walls of their minutest divisions.

207. In every one of these cases, we find ihefiee aspect of the pri-
mary membrane in contact with cells, which form a more or less con-
tinuous layer upon its surface. These cells can only receive their
nutriment by the imbibition of fluid, through the primary membrane,
from the blood brought to its attached surface by the capillary ves-
sels of the tissue with which it is in relation. Thus in the skin and
mucous membranes, a very copious supply of blood is brought to the
attached surface of the primary membrane, by the minutely-distributed
capillaries which form a large part of the subjacent tissue ; and it is
from these that the epidermis and epithelium draw their nourishment,
through the primary membrane. In like manner, the ultimate follicles

BASEMENT OR PRIMARY MEMBRANE. 135

and tubuli of the glands are surrounded by a copious network of
capillaries (Fig. 10) ; and it is from these, through the primary mem-
brane, that the cells of these follicles draw their nourishment. Hence
this membrane, in every instance, forms a complete septum, on the one
hand between the stream of blood in the vessels and the surround-
ing tissues, since it forms the lining even of the minutest capillaries ;
and on the other between the fluids in the interstices of the substance
of the true skin, the mucous membranes, &c., and the cells covering
their free surfaces. It is evident, therefore, that whilst bounding
th^se tissues and restraining the too free passage of fluids from their
surfaces, it allows the transudation of a suflScient amount for the nu-
trition of the cells which lie upon it; and, as we shall presently see,
these cells frequently pass through all their stages of growth so rapidly,
that a very free supply of nutriment must be required by them.
Hence, notwithstanding its apparent homogeneousness, the primary
membrane must have a structure which readily admits the passage of
fluid. In this respect it corresponds with the membrane, which forms
the wall of the cells of both Animal and Vegetable tissues ; for this
also appears completely homogeneous and structureless, when seen
under its simplest aspect, and yet allows the free passage of fluids
from one cell to another.

208. But it is probable that this membrane performs a much more
important office than that of simply limiting the fluids, whilst allow-
ing the requisite transudation. We cannot account for the new pro-
duction of cells, which (as will presently appear) is continually taking
place on its surface, without referring to it as the originator of these
cells, — that is, as the source of their germs. The new generations of
cells cannot here be developed by the reproductive powers of the old
ones (§211); since the latter are often completely cast off* entire,
before they can liberate the reproductive granules ; or they undergo
changes which evidently unlit them for such a purpose. Thus in the
Epidermis we shall find that they become flattened into dry scales,
forming an almost horny layer on the* surface of the body ; whilst the
new cells are originating beneath, from the surface of the basement-
membrane (§ 224 and Fig. 16). Hence we cannot find any other
origin for these cells than in the basement-membrane itself; and there
seems every probability that the granules, which have been mentioned
as being frequently diffused through it, are in reality
the germs of cells to be developed from its surface ; Fig. is.

whilst the distinct spots are collections of similar
granules, each of which may give origin to a large
number of such cells, which spring from them as
from a centre. We shall presently see that these _

'' germinal centres" closely resemble the nuclei of component ceiis
cells in general, from which it is unquestionable that ^^ primary mem-

r n • /c- ^r^ rr«i 1 i-^ brane, with adhe-

new crops ot cells may arise (§ 250). ihe only dii- rem epitUeUai ceus.

ference is, that in the latter case, the groups of new

cells are for a time contained within the parent-cell (Fig. 30) ; whilst

136 SIMPLE ISOLATED CELLS.

in the former, they are developed on the free surface of the base-
ment membrane. In Fig. 13 is shown a portion of the same mem-
brane as that represented in Fig. 12 ; but having been rendered
transparent by acetic acid, its real nature as a layer of flattened nu-
cleated cells is more obvious; the nucleus or germinal spot of the
central cell has given origin to a cluster of oval epithelial cells, of
which five still adhere to it.

209. Hence w^e are probably to regard this primary or basement
membrane as transitional, rather than a permanent structure ; and to
look upon it as furnishing the germs of all the cells, which are de-
veloped upon its surface; as well as the medium, through which they
are supplied wdth nutriment. It must be continually undergoing
disintegration, therefore, on itsyree surface; and must be as continu-
ally renewed, at the side in relation with the blood-vessels.

4. Of Simple Isolated Cells, employed in the Organic Functions.

210. The active functions of the Animal body are performed, to a
much greater extent than was until lately believed, by the agency of
simple isolated cells; of which every one grows and lives quite inde-
pendently of the rest, just as if it were one of the simplest cellular
plants (§ 30); but of w^hich all are dependent upon the general nu-
tritive fluid for the materials of their development, imbibing it from
the currents that circulate in their neighbourhood. It may be said,
indeed, that all the Vegetative functions of the body, — all the pro-
cesses of Nutrition and Reproduction, — all those operations, in short,
which are common to Plants and Animals, — are performed in the
Animal and Vegetable structures by the very same means, the agency
of cells; and this is true, not only of the healthy actions, but of vari-
ous morbid operations, in which the unusual development of cells,
possessing peculiar endowments, performs a most conspicuous part.
Hence it will be necessary to enter somewhat at large into the history
of cell-development in the Anit^ial body ; and the various modifica-
tions under which this process may take place. In fact, a knowledge
of the Physiology of Cells may be regarded as the foundation of all
accurate acquaintance with that department of the Science, which
relates to the Nutritive and Reproductive processes; and it has a con-
siderable bearing, as we shall see hereafter, upon the history of the
purely Animal functions.

211. The history of the Animal cell, in its simplest form, is pre-
cisely that of the Vegetable cell of the lowest kind. It lives for
itself and by itself; and is dependent upon nothing but a due supply
of nutriment, and of the appropriate stimuli, for the continuance of
its growth and for the due performance of all its functions, until its
term of life is expired. It originates from a reproductive granule,
previously formed by some other cell ; this granule attracts to itself,
assimilates, and organizes, the particles of the nutrient fluid in its
neio-hbourhood ; converts some of them into the substance of the

SIMPLE ISOLATED CELLS.— LYMPH-CORPUSCLES. 137

cell-wall, whilst it draws others into the cavity of the cell ; in this
manner the cell gradually increases in size ; and whilst it is itself
approaching the term of its life, it usually makes
preparation for its renewal, by the development Fig. u.

of reproductive granules in its interior, which ~

may become the germs of new cells, when set
free from the cavity of the parent. There is an
important difference, however, in the endow-
ments of the Animal and Vegetable cell. We
have seen that the latter can in general obtain
its nutriment, and the materials for its secretion,
by itself combining the inorganic elements into
organic compounds. The former, however, is simple isolated ceiis. con-
totally destitute of this power ; it can produce no "^ reproductive moie-
organic compound, and we have yet to learn how
far its power of transforming one compound into another may extend ;
and its chief endowment seems to be that of attracting or drawing to
itself some of the various substances, which are contained in the
nutritive fluid in relation wdth it. This fluid, as we shall see here-
after, is a mixture of a great number of compounds ; and different
sets of cells appear destined severally to appropriate these, just as
the different cells of a parti-coloured flower have the power of draw-
ing to themselves the elements of their several colouring matters.
As far as is yet known, however, the composition of the cell-wall
is everywhere the same ; being that of Proteine. It is in the nature
of the contents of the cell, that (as among the cells of Plants) the
greatest diversity exists ; and we shall find that the purposes of the
different groups of cells, in the Animal economy, depend upon the
nature of the products they secrete, and upon the mode in which
these products are given back after they have been subjected to the
action of the cells.

212. The very simplest and most independent condition of the
Animal Cell is probably to be found in the Blood, the Chyle, and the
Lymph ; in all of which liquids we meet with floating cells, which
are completely isolated from one another, and which are consequently
just as independent as the vesicles of the Red Snow or other simple
cellular Plants. Indeed in the nature of their habitat^ we may com-
pare them with the Yeast- Plant; for as this will only vegetate in a
saccharine fluid containing vegetable albumen, so do we find that
these floating cells will only grow and multiply in the albuminous
fluids of animals. In their general appearance they very closely cor-
respond with the figure already given as the type of the simple cell.
Their diameter is pretty uniform in the different fluids of the body,
and even in different animals ; being for the most part about l-3000th
of an inch. They are sometimes nearly spherical, and sometimes
flattened -, when they present the latter shape, they may be made to
swell out into the spherical form (see Frontispiece^ i^igs. 4 and 5), by
the action of water, which they imbibe according to the laws of En-
dosmose, — the thinner fluid, water, passing towards the more viscid

138 COLOURLESS CORPUSCLES OF BLOOD, LYMPH, AND CHYLE.

contents of the cell, and mingling with them. By the continuance of
this kind of action, the cell will be caused to burst. These cells,
which are known as the corpuscles of the Chyle and Lymph, and as
the White Corpuscles of the Blood, are observed to contain a num-
ber of minute molecules in their interior {Front. Fig. 4); and at a
certain stage of their development, — probably that which immediately
precedes the maturation and rupture of the parent-cell, — these mole-
cules may be seen, with a good Microscope, in active movement
within the cavity. The action of a very dilute solution of potash
causes the immediate rupture of these cells, and the discharge of the
contained molecules, which are probably the germs of new cells of a
similar character. And when they rupture spontaneously, which
they are much disposed to do under the influence of contact with air,
the fluid which they set free shows an obvious tendency to assume a
fibrous arrangement.

213. There is reason to think that these cells have for their office
the transformation of Albumen into Fibrin ; that is to say, the ela-
boration of the spontaneously-coagulating and fibrillating substance,
from the mere chemical compound which forms the raw material of
the Animal tissues. For we find these cells in every situation in
which we know the transformation to be going on ; and we observe
their number to bear a close relation with the amount of fibrin pro-
duced in the fluid. Thus in the Inflammatory process, the quantity
of fibrin in the blood is very greatly augmented ; and the number of
white corpuscles found in that fluid, when it is drawn from the body,
is very largely increased. Moreover they are observed to accumulate
in great numbers in the vessels of inflamed parts ; and not only in
these, but in all parts where processes of growth and reparation are
going on, which require a large supply of highly-elaborated fibrin.
They are found, too, in the exudations of fibrinous matter, poured out
from the blood upon wounded or inflamed surfaces ; and here they
show the very same properties as the w^hite or colourless corpuscles
of the blood, — that is, they exhibit moving molecules in their inte-
rior ; they burst and emit these when brought in contact with an alka-
line solution ; and their fluid contents show a
disposition to fibrillate, when they are not al-
tered by any chemical reagent. Hence it may
be concluded that they belong to the same
class of cells ; being probably developed from
granular germs set free from the blood, along
with the matter of the fibrinous exudation itself.
214. The history of the simple Animal cell
corresponds, therefore, in all essential parti-
culars with that which has been already de-
scribed as the simplest form of Life or Vital
Activity ; but we now see how the separate
Colourless cells, with.factive Hfc of the individual cells is made to contri-
Sn'i^iTpesftPaiis!^ ""^ ^^''"' butc to the general life of the entire organism,

Fig. 15.

COLOURLESS AND RED CORPUSCLES OF BLOOD. 139

and is at the same time dependent upon it. If the nutrient material
were not prepared by other processes, these cells could not exist; on
the other hand, if this nutrient material were not further elaborated
by their action, no subsequent processes of growth could take place.
The compounds which are formed as products of secretion in the
simple Vegetable cell, are given back to the external world from
which their materials were drawn, when that cell ceases to exist; to
be used, perhaps, in the general economy of nature, as the material
for some other and higher structure. But when such cells themselves
form a portion of a higher and more complex fabric, whether of the
Plant or Animal, the substances they yield back as the products of
their action, are made use of in some other set of processes in the
economy of the same being. Thus the fibrin-elaborating cells, of
which we have been speaking, appear to be continually growing,
dying, and reproducing themselves ; drawing albumen from the fluid
in which they float, and returning it as fibrin, to supply the constant
drain of that substance, which is occasioned by the nutritive opera-
tions.

215. Besides the cells already mentioned, the blood of Vertebrated
animals also contains others, which are distinguished by their red
colour and flattened form. These are equally isolated, and lead an
independent life ; undergoing all their changes whilst floating in the
rapidly-circulating current. These Red Corpuscles are found but
very sparingly in the blood of invertebrated animals ; and only in that
of the higher clavSses. Their proportion in the blood of Vertebrata
varies considerably in the several groups of that sub-kingdom ; and
seems to be closely connected with the relative activity of respiration
in each case. They present, in every instance, the form of a flattened
disk, which is circular in Man and in most Mammalia {Front. Fig. 1),
but which is oval in Birds, Reptiles, and Fishes, and in a few Mam-
mals (Front. Fig. 6). This disk is in both instances a flattened cell,
whose walls are pellucid and colourless, but whose contents are co-
loured. Like the corpuscles already described, they may be caused
to swell up and burst, by the imbibition of water ; and the perfect
transparency and the homogeneous character of their walls then be-
come evident. (Front. Fig. 8, e.) These red corpuscles are not only
distinguished from the others by the colour of their contents; they are
also characterized by the absence of the separate molecules, which
formed so distinctive a feature in the preceding; and in Oviparous
Vertebrata by the presence of a distinct central spot or nucleus. This
nucleus appears to be composed of an aggregation of minute granules,
analogous to those which are elsewhere diffused through the interior
of the cell ; and it is undoubtedly the source from which new cells
may originate within the parent, as will be presently explained. The
nucleus (where it exists) may be easily obtained separate from the
cell- wall and its contents, by treating the red corpuscles with water.
The first effect of this is to render the nucleus rather more distinct, as
is seen by contrasting the corpuscle which has been thus slightly acted

14Q RED CORPUSCLES OF BLOOD.

on {Front. Fig. 8, «), with the unaltered corpuscle [Front. Fig. 6) of
the same animal. After a short time, the corpuscle swells out and
becomes more circular {Front. Fig. 8, h)\ and in a short time longer,
the nucleus is seen, not in the centre of the disk, but near its margin
(Front. Fig. 8, c, d). Finally, the wall of the cell ruptures ; the nu-
cleus and its other contents are set free ; and whilst the colouring
matter is diffused through the surrounding fluid, the cell-walls and
the nuclei are separately distinguishable. {Front. Fig. 8, e.)

216. It is remarkable, however, that the red corpuscles of the blood
of Mammals should possess no obvious nucleus ; the dark spot which
is seen in their centre {Front. Fig. 1), being merely an effect of refrac-
tion in consequence of the double-concave form of the disk. When
the corpuscles are treated with water, so that their form becomes first
flat, and then double-convex, the dark spot disappears ; whilst, on
the other hand, it is made more evident when the concavity is in-
creased by the partial emptying of the cell, which may be accomplished
by treating the blood-corpuscles with fluids of greater density than
their own contents. Observers are much divided upon the question,
whether or not the blood-disks of Mammals really contain a nucleus.
There seems every probability, from analogy, that a nucleus exists in
them as in all other red corpuscles ; but it cannot be brought into
view by any ordinary method. Dr. G. O. Rees states, however, that
by carefully examining the deposit at the bottom of water through
which red corpuscles had been diffused, he could distinguish appear-
ances that indicated the existence of nuclei ; although they escape
observation when within the corpuscles themselves, on account of
their high refractive power. He describes them as being circular
and flattened like the red corpuscles themselves ; and about two-
thirds their diameter.

217. The size of the Red Corpuscles is not altogether uniform in
the same blood ; thus it varies in that of Man from about the l-4000th
to the l-2800th of an inch. But we generally find that there is an
average size, which is pretty constantly maintained among the differ-
ent individuals of the same species ; that of Man may 6e stated at
about l-3400th of an inch. The round corpuscles of the Mammalia
do not in general depart very widely from this standard ; except in
the case of the Musk-Deer, in which they are less than l-12000th of
an inch in diameter. It is in the Camel tribe alone that we find
oval corpuscles among Mammals : these have about the same average
length as the round corpuscles of Man, but little more than half the
breadth. — In Birds, the corpuscles are occasionally almost circular ;
but in general their diameters are to each other as 1 J or 2 to 1. The
size of the corpuscles is usually greater according to the size of the
Bird ; thus among the Ostrich tribe, the long diameter is about
l-1650th of an inch, and the short diameter l-3000th ; whilst among
the small Sparrows, Finches, &c., the long diameter is about l-2400th,
and the short frequently does not exceed half that amount.

218. It is in Reptiles that we find the largest red corpuscles ; and

RED CORPUSCLES OF BLOOD. 141

it is in their blood, therefore, that we can best study the characters of
these bodies. The blood-discs of the Frog, from the facility with
which they maybe obtained, are particularly suitable for the purpose ;
their long diameter is about the 1-lOOOth of an inch, whilst their
short or transverse diameter is about 1-I800th. The curious Proteus,
Siren, and other allied species, which retain their gills through their
whole lives, are distinguished by the enormous size of their blood-
disks. The long diameter of the corpuscles of the Proteus is about
l-337th of an inch ; they are consequently almost distinguishable with
the unaided eye. The long diameter of the corpuscles of the Siren
is about l-435th of an inch, and their short diameter about l-800th ;
the long diameter of the nuclei of these corpuscles is about 1-lOOOth,
and the short diameter about l-2000th of an inch, — so that the
nuclei are about three times as long, and nearly twice as broad as
the entire human corpuscles.

219. There can be little doubt that the Red Corpuscles go through
the same history as other cells ; and there is evidence that they are
rapidly regenerated, under favourable circumstances, when a large
number of them have been lost. When much blood has been drawn
from the body, the proportion of red corpuscles in the remaining fluid
is at first considerably lowered : since the fluid portion of the blood is
replaced almost immediately, whilst these floating cells require time
for their regeneration. Their amount progressively increases, how-
ever, until it has reached its proper standard, provided that a due
supply of the materials be afforded. We shall presently see that one
of these materials is Iron ; and it is well known that iron administered
internally is an important aid in recovery from severe hemorrhages, as
well as a valuable remedy for certain constitutional states, in which
there is a diminished power of producing red corpuscles. Thus in
Chlorosis, under the administration of iron, the amount of red cor-
puscles in the blood has been doubled within a short period. Hence
there can be no doubt that the Red Corpuscles are produced from
germs, and grow like other cells, under circumstances favourable to
their development ; and it is probable that, in the healthy state of the
system, the constant production, and the constant death and disin-
tegration, balance one another. In some instances (as in Chlorosis)
the production is not sufficient to make up for the loss by death ; and
the total amount in the blood undergoes an extraordinary diminution,
sometimes even to less than a quarter of their proper proportion. In
other cases, under the influence of excessive nutriment (as in the
state termed Plethora), the proportion of Red Corpuscles is increased
beyond the normal amount ; and in this condition, the loss of a small
quantity of blood may be a preservative from the evils to which it is
incident, from Hemorrhage of various kinds.

220. The precise mode in which the Red Corpuscles are usually de-
veloped, has not yet been positively determined ; and there is still a
degree of uncertainty with respect to their parentage, — in other words,
as to the source of their primitive germs. In the fluid withdrawn from

3y< SIMPLE ISOLATED CELLS.— BLOOD-CORPUSCLES.

the heart of the embryo chick about the third day, the whole process
of the formation of the oval red corpuscles from minute granules has
been distinctly traced ; and there is every probability that these gra-
nules are cell-germs set free by some of the cells of the primary embry-
onic structures, which thus originate blood-corpuscles, in the same
manner as other cells originate bone, nerve, muscle, &c. The subse-
quent increase and constant maintenance of the number of red corpus-
cles, can scarcely be due to any other process, than that by which simi-
lar isolated cells are regenerated; that is, by the continual production
of new generations by germs prepared by the parent. According to
the celebrated Leeuwenhoek, certain red corpuscles are occasionally
seen to divide themselves into six, which, at first very small, gradu-
ally increase to the size of their parents ; and this observation has
been confirmed by Dr. Barry, w^ho regards the multiplication as due
to the development of six young cells, which sprout from the circum-
ference of the nucleus, and grow at first within the cell-wall of the
parent, but afterwards rupture it, and become free. On the other
hand, Dr. G. O. Rees affirms, that, when examining a portion of
blood maintained at about its natural temperature, he observed some
of the corpuscles to assume an hour-glass form, by a contraction
across their middle ; and that, by the increase of this contraction,
producing the division of the corpuscles, two unequal-sized circular
bodies were eventually produced from each ; which, when treated
with a strong saline solution, were emptied of their contents, like
ordinary blood-disks. It can scarcely be doubted that, in one of
these modes, the Red corpuscles reproduce themselves; and that in this
manner a continual succession is kept up. Some have supposed that
the Red corpuscles originated from the White or colourless corpuscles
previously described ; but this idea seems to have little other foun-
dation, than the correspondence in size between the colourless cor-
puscles of the Frog's blood, and the nuclei of its red corpuscles.
This correspondence is quite accidental, however; for in Man, the
colourless corpuscles are somewhat larger than the entire red disks ;
in the Musk-deer, they are far larger; and in the Proteus they are far
smaller than the nuclei of the latter. For the diameter of the Colour-
less corpuscle varies extremely little ; whilst that of the red, as we
have seen, has a range from 1-337 th of an inch to less than
l-12,000th.

221. The Chemical composition of the walls and nuclei of the Red
corpuscles is very different from that of their contents. The substance
of the former has been termed Glohuline ; but it does not seem to
differ in any essential character from other substances resulting from
the organization of the proteine-compounds. The compound which
forms the contents of the red corpuscles, however, and gives them
their characteristic hue, is altogether peculiar, and has received the
name of Hcematine. Its composition is notably different from that of
the proteine-compounds ; the proportion of Carbon to the other ingre-
dients being very much greater; and a definite quantity of iron being

\

SIMPLE ISOLATED CELLS.— BLOOD-CORPUSCLES. 143

an essential part of it. Its formula is 44 Carbon, 22 Hydrogen, 3
Nitrogen, 6 Oxygen, and 1 Iron. When completely separated from
albuminous matter, it is a dark brown substance, incapable of coagu-
lation, nearly insoluble in water, alcohol, ether, acids, or alkalies,
alone ; but readily soluble in alcohol mixed either w^ith sulphuric acid
or ammonia. The solution, even when diluted, has a dark colour;
and possesses all the properties of the colouring matter of venous
blood. The iron may be separated from the hasmatine by strong re-
agents which combine with the former, and the latter still possesses
its characteristic colour. This hue cannot be dependent, therefore,
on the presence of iron in the state of peroxide ; as some have sup-
posed. On the other hand, the iron is most certainly united firmly
with the ingredients of the hsematine, as contained in the red corpus-
cles; for this may be digested in dilute sulphuric or muriatic acid for
many days, without the least diminution in the quantity of iron, the
usual amount of which may be afterwards obtained by combustion
from the hsematine that has been subjected to this treatment. This
experiment seems further to prove, that the iron cannot be united
with the hsematine in the state of either protoxide or peroxide, as
maintained by Liebig; since weak acids would then dissolve it out.

222. Regarding the nature of this compound, and the changes w^hich
it undergoes in respiration, there is still much to be learned ; and
until these points have been more fully elucidated, the precise uses of
the red corpuscles in the animal economy cannot be understood.
There is evidence, however, that the production of Hsematine is (like
the production of the red colouring matter of the Protococcus nivalis,
§ 31), a result of chemical action taking place in the cells them-
selves; for no substance resembling Hsematine can be found in the
liquid in which these cells float, and scarcely a trace of iron can be
detected in it; whilst, on the other hand, the fluid portion of the
chyle holds a large quantity of iron in solution, which seems to be
drawn into the red corpuscles, and united with the other constituents
of hsematine, as soon as ever it is delivered into the circulating cur-
rent. The colouring matter appears to exist in two states, the pre-
cise chemical difference between which has not yet been ascertained.
In arterial blood it is a florid scarlet; w^hilst in venous blood it is of
a purpler hue. By circulating through the capillaries of the system,
the arterial or bright hsematine becomes converted into dark or ve-
nous hsematine ; and the converse change takes place in the capillaries
of the lungs, the original florid hue being recovered. Now it is cer-
tain that the blood, in its change from the arterial to the venous con-
dition, loses oxygen, and becomes charged with an increased amount
of carbonic acid, although its precise mode of combination is not
known ; on the other hand, in its return from the venous to the arte-
rial state, the blood gives off" this additional charge of carbonic acid,
and imbibes oxygen. The change of colour, under similar con-
ditions, takes place out of the body, as well as in it. Thus if
venous blood be exposed for a short time to the air, its surface

144 SIMPLE ISOLATED CELLS.— BLOOD-CORPUSCLES.

becomes florid ; and the non-extension of this change to the interior of
the mass is evidently due to the impossibility of bringing air into rela-
tion with every particle of the blood, in the manner in which the lungs
are so admirably contrived to effect. If venous blood be exposed to
pure oxygen, the change of colour will take place still more speedily;
and it is not prevented by the interposition of a thick animal mem-
brane, such as a bladder, between the blood and the gas. On the
other hand, if arterial blood be exposed to carbonic acid, it loses its
brilliant hue, and is rendered as dark as venous blood; or even darker,
if exposed very completely to its influence. The simple removal of
this carbonic acid is not sufficient to restore the original colour ; for
this removal may be effected by hydrogen, which has the power of dis-
solving out (so to speak) the carbonic acid diffused through the blood,
without the restoration of the arterial hue, unless oxygen be present,
or saline matter be added to the blood.

223. These changes in the condition of the contents of the Red
corpuscles, taken in connection with the fact, that these bodies are
almost completely restricted to the blood of Vertebrata, (whose respi-
ration is much more energetic than that of any Invertebrated animals
save Insects, which have a special provision of a different character,)
and that their proportion to the whole mass of the blood corresponds
with the activity of the respiratory function, — leave little doubt that
they are actively (but not exclusively) concerned as carriers of Oxygen
from the lungs to the tissues, and of Carbonic acid from the tissues to
the lungs ; and that they have no other direct concern in the functions
of Nutrition, than the fulfilment of this duty. Their complete absence
in the lower Invertebrated animals, in the earliest condition of the
higher, and in newly-forming parts until these are penetrated by blood-
vessels, seems to indicate that they have no immediate connection
with even the most energetic operations of growth and development ;
whilst, on the other hand, there is abundant evidence, that the normal
activity of the animal functions is mainly dependent upon their pre-
sence in the blood in due proportion.

224. Next in independence to the cells or corpuscles floating in the
animal fluids, are those which cover the free membranous surfaces of
the body, and form the Epidermis and Epithelium. Between these
two structures there is no more real difference, than there is between
the Skin and the Mucous membranes. The one is continuous with
the other; they are both formed of the same elements; they are cast
off and renewed in the same manner ; the history of the life of the
individual cells of each is nearly identical ; but there is an important
difference in the purposes, which they respectively serve in the gene-
ral economy. The Epidermis or Cuticle covers the exterior surfaces
of the body, as a thin semi-transparent pellicle, which is apparently
homogeneous in its texture, is not traversed by vessels or nerves, and
was formerly supposed to be an inorganic exudation from the surface
of the true Skin, designed for its protection. It is now known, how-
ever, to consist of a series of layers of cells, which are continually

SIMPLE ISOLATED CELLS.— EPIDERMIS. 145

wearing off at the external surface, and are being renewed at the
surface of the true skin ; so that the newest and deepest layers gradu-
ally become the oldest and most superficial, and are at last thrown off
by slow desquamation. Occasionally this desquamation of the cuticle
is much more rapid ; as after Scarlatina and other inflammatory affec-
tions of the Skin.

225. In their progress from the internal to the external surface of
the Epidermis, the cells undergo a series of well-marked changes.
When we examine the innermost layer, we find it soft and granular;
consisting of nuclei, in various stages of development into cells, held
together by a tenacious semi-fluid substance. This was formerly
considered as a distinct tissue, and was supposed to be the peculiar
seat of the colour of the skin ; it received the designation of rete
mucosum. Passing outwards, we find the cells more completely
formed ; at first nearly spherical in shape ; but becoming polygonal
where they are flattened against one another. As we proceed further
towards the surface, we perceive that the cells are gradually more
and more flattened, until they become mere

horny scales, their cavity being obliterated ; ^'o i^-

their origin is indicated, howcA^er, by the ^t-- - -^~^^

nucleus in the centre of each. This flattening -
appears to result from the gradual desiccation

or drying-up of the contents of the cells, which ' J^

results from their exposure to the air. Thus ^ ,^

each cell of the Epidermis is developed from ^S^^^^^m

the nucleus on the surface of the basement '^^\<^s~*^

membrane, (which nucleus is probably fur- '^ ^ ^9^

nished by the membrane itself, § 208,) and is ^ c^'S Cr^

gradually brought to the surface by the deve- ^(SM^^ml.

lopment of new cells beneath, and the removal ~^^^^fe^^^/^

of the superficial layers ; whilst at the same ^, ^^'^'^'^^^~^~^,

. . * • 1 1 ^ • r •! Oblique section of Epider-

tirae it is progressively changed in lorm, until mis, showing uie progressive

it is converted into a flattened scale. The cdi^firnuciL'resSnlTpTu

accompanying representation of an oblique iJiLrnSef L^rr^ee'/rbe'

section of the Epidermis, exhibits the principal gradually developed into ceiis,

, . r' 1 at 0. c, and a,- and the ceils are

gradations OI its component structures. flattened into lamellae. forming

226. The Epidermis covers the whole ex- ^^--^eno;^ portion of the ep.
terior surface of the body ; not. excepting the

Conjunctiva of the eye, on which, however, it has more the character
of an Epithelium ; and the Cornea, on which it participates in the
horny character of the Epidermic covering of the skin. The con-
tinuity is well seen in the cast skin or slough of the Snake ; in which
the covering of the front of the eye is found to be as perfectly exu-
viated, as that of any part of the body. The number of layers varies
greatly in different parts; being usually found to be the greatest,
where there is most pressure or friction. Thus on the soles of the
feet, particularly at the heel and the ball of the great toe, the Epi-
dermis is extremely thick ; and the palms of the hands of the labouring
10

146

SIMPLE ISOLATED CELLS.— EPIDERMIS.

Horny Epidermis, from conjunctiva covering
the cornea; a, single scales; b, simple lamina
of epithelium; below is seen a double layer of
the same.

raan are distinguished by the increased density of their horny cover-
ing. It would seem as if the irritation of the Skin stimulated it to an
increased production of this substance. The Epidermic membrane

is pierced by the excretory ducts
^'^•^^- of the sweat glands, and of the

sebaceous follicles, which lie in the
true skin and immediately beneath
it ; or we should rather say that it
is continuous with the delicate epi-
thelial lining of these. — The JYails
may be considered as nothing more
than an altered form of Epidermis.
When examined near their origin,
they are found to consist of cells
which gradually dry into scales;
and these remain coherent together.
A new production is continually
taking place in the groove of the
skin, in which the root of the nail
is imbedded ; and probably also from the whole subjacent surface.

227. The Epidermis, when analyzed, is found to differ from the
proteine-compounds in its composition ; but not in any very striking
degree. The proportion of its elements is considered to be 48 Carbon,
39 Hydrogen, 7 Nitrogen, 17 Oxygen ; and this corresponds exactly
with the composition of the substance of which Nails, Horn, Hair and
"Wool are constituted. It seems probable, however, that the cell-walls
are formed, as elsewhere, of Fibrin; and that the horny matter is a
secretion in their interior, which is drawn from the elements of blood
during their growth and development.

228. The Epidermis appears solely destined for the protection of
the true Skin ; both from the mechanical injury and the pain, which
the slightest abrasion would produce ; and from the irritating effects
of exposure to the external air, and of changes of temperature. We
perceive the value of this protection, when the Epidermis has been
accidentally removed. It is very speedily replaced, how^ever ; the
increased determination of blood to the Skin, which is the conse-
quence of the irritation, being favourable to the rapid production of
Epidermic cells on its surface.

229. Mingled with the Epidermic cells, we find others which se-
crete colouring matter instead of horn ; these are termed Pigment- cells.
They are not readily distinguishable in the epidermis of the White
races, except in certain parts, such as the areola around the nipple,
and in freckles, nsevi, &c. But they are very obvious, on account of
their dark hue, in the newer layers of the Epidermis of the Negro
and other coloured races ; and, like the true Epidermic cells, they
dry up and become flattened scales in their passage towards the sur-
face, thus constantly remaining dispersed through the Epidermis, and
giving it a dark tint Avhen it is separated and held up to the light.

SIMPLE ISOLATED CELLS.— PIGMENT CELLS.

147

In all races of men, however, we find the most remarkable develop-
ment of Pigment-cells on the inner surface of the Choroid coat of the
eye, where they form several
layers, known as the Pigmentum Fig. is.

nigrum. Here they have a very
regular arrangement, which is best
seen where they cover the blood-
vessels of the Choroid coat in a
single layer, as shown in Fig. 18.
When examined separately, they
are found to have a polygonal
form (Fig. 19, a), and to have a
distinct nucleus (6) in their inte-
rior. The black colour is given
by the accumulation, within the
cell, of a number of flat, rounded
or oval granules, measuring about
l-20,000th of an inch in diameter,
and a quarter as much in thick-
ness ; these, when separately
viewed, are observed to be trans-
parent, not black and opaque ; and they exhibit an active movement
when set free from the cell, and even whilst enclosed within it. The
pigment-cells are not always of a simple rounded or
polygonal form; they sometimes present remarkable stel-
late prolongations, under which form they are well seen
in the skin of the Frog. — The Chemical nature of the
black pigment has not yet been made evident; it has
been shown, however, to have a close relation with that
of the Cuttle-fish ink or Sepia, which derives its colour
from the pigment-cells lining the ink-bag ; and to include
a larger proportion of Carbon than most other organic
substances, — every 100 parts containing 581 of this
element.

230. That the development of the Pigment-cells, or at least the
formation of their peculiar secretion, is in some degree due to the
influence of Light, seems evident from the facts already mentioned
(§ 93). To these it may be added, that the new-born infants of the
Negro and other dark races do not exhibit nearly the same depth of
colour in their skins, as that which they present after the lapse of a
few days ; which seems to indicate that exposure to light is necessary
for the full development of the characteristic hue. An occasional
development of dark pigment-cells takes place during pregnancy in
some females of the fair races ; thus it is very common to meet with
an extremely dark and broad areola round the nipple of pregnant
women ; and sometimes large patches of the cutaneous surface, on the
lower part of the body especially, become almost as dark as the skin
of the Negro. On the other hand, individuals are occasionally se^n

A portion of the choroid coat from the eye of the
Ox, showing the pigment-cells, where they cover
a, a, a, the veins, in a single layer; &, b, ramifi-
cations of the veins near the ciliary ligament,
covered with less regular pigment-cells ; c, c,
spaces between the vessels, more thickly covered
with pigment-cells.

Fig. 19.

%

Caopuscles of
Pigment, magni-
fied 300 diame-
ters;—a, cell; b,
nucleus.

%4B SIMPLE ISOLATED CELLS.— EPITHELIUM.

with an entire deficiency of pigment-cells, or at least of their proper
secretion, not merely in the skin, but in the eye ; such are termed
Albinoes ; and they are met with as well among the fair, as among
the dark races. The absence of colour usually shows itself also in
the hair, which is almost white.

231. The Epithelium may be designated as a delicate cuticle,
covering the free internal surfaces of the body ; and apparently de-
signed, in some instances, simply for their protection; whilst in other
cases, as we shall presently find, it serves purposes of far greater
importance. It has long been known that the Epidermis might be
traced continuously from the lips to the mucous membrane of the
xnouth, and thence down the (Esophagus into the stomach; and that
in the strong muscular stomach or gizzard of the granivorous birds,
it becomes quite a firm horny lining. But it has been only ascer-
tained by the use of the Microscope, that a continuous layer of cells
may be traced, not merely along the whole surface of the mucous
membrane lining the alimentary canal, but likewise along the free
surfaces of all other Mucous membranes, with their prolongations into
follicles and glands ; as well as on Serous and Synovial membranes,
and the lining membrane of the heart, blood-vessels, and absorbents.
The Epithelial cells, being always in contact with fluids, do not dry
up into scales like those of the Epidermis; and they differ from them
also in regard to the nature of the matter, which they secrete in their
interior. In this respect, however, the Epithelial cells of different
parts are unlike one another; fully as much as any of them are unlike
the cells of the Epidermis ; for we shall find that all the secretions of
the body are the product of the elaboration of Epithelium cells ; and
consequently there are as many varieties of endowment, in these im-
portant bodies, as there are varieties in the result of their action.

232. The Epithelium covering the Serous and Synovial mem-
branes, and the lining of the blood-vessels, is composed of flattened
polygonal cells, (resembling those shown in Fig. 20,) lying in appo-
sition with each other, so as to form a kind of pavement ; hence this
form is termed pavement or tesselated-Epithelmm. There is no reason
to believe that it possesses any active endowments in these situations;
since it does not appear to be concerned in the elaboration of any
peculiar secretion. It has been already pointed out (§ 196), that the
fluid of serous membranes is separated from the blood by a simple act
of mechanical transudation, (which often takes place to a great extent
after death ;) the walls of the blood-vessels do not appear to be con-
cerned in forming any peculiar secretion; and the only product of this
kind, which indicates any special endowment in the epithelium-cells,
is the synovia, which is probably elaborated by the cells covering
the vascular fringes of the synovial membrane, formerly mentioned
(§ 197). The cells draw it from the blood, during the progress of
their growth, form it as a secretion within themselves, and then cast
it into the general cavity of the joint, (when their term of individual
life is ended,) either by the rupture or the liquefaction of their walls.

SIMPLE ISOLATED CELLS.— EPITHELIUM.

149

In other cases, it would seem as if the epithelial cells were not fre-
quently cast otf and renewed, but possessed a considerable perma-
nency. It is to be remembered that, in the healthy state of the serous
and synovial membranes, and in that of the lining membrane of the
blood-vessels and absorbents, they are entirely secluded from sources
of irritation ; and that they lead a sort of passive life, very different
from the active life of the mucous membranes. In fact, it would
appear to be the sole object of the serous membranes, to enclose and
suspend the viscera, in such a manner as to allow of the access of
blood-vessels, nerves, gland-ducts, &c. ; and at the same time to
permit them the required freedom of motion, and to provide against
the irritation of opposing parts, by furnishing an extremely smooth
and moistened surface, wherever friction takes place. Hence we
find membranes, with all the characters of serous surfaces, in the
false joints formed by ununited fractures, and in other similar
situations.

233. The Epithelium of the Mucous membranes and their pro-
longations is found under two principal forms, the tesselated, and the
cylindrical. An example of the Tesselated form is shown in Fig. 20,

Fiar. 21.

Separated Epithelium-cells, a, with
miclei, b. and nucleoli, c, from mucous
membrane of mouth.

Pavement-Epithelium of the
Mucous Membrane of the small-
er bronchial tubes; a, nuclei with
double nucleoli.

which shows the separate epithelium-cells of the mucous membrane
of the mouth, as they are frequently met with in saliva. The cells
are not always so polygonal in form, however ; sometimes retaining
their rounded or oval form, and being separated by considerable
interstices, so that they can scarcely be said to form a continuous
layer. A specimen of this kind is seen in Fig. 21, which represents
a group of epithelium-cells from one of the smaller bronchial tubes.
This form of tesselated epithelium is more commonly met with, where
the secreting operations are more active, the life of the cells conse-
quently shorter, and the renewal of them more frequent ; so that they
have not time, so to speak, to be developed into a more continuous
layer. — The Cylinder-Epithelium is very differently constituted. Its
component cell are cylinders, which are arranged side by side ; one
extremity of each cylinder resting upon the basement-membrane,
whilst the other forms part of the free surface. The perfect cylin-
drical form is only shown, when the surface on which the cylinders
rest is flat or nearly so. When it is convex, the lower ends or base-

150

SIMPLE ISOLATED CELLS.— EPITHELIUM.

Fig. 22.

//

ments of the cells are of much smaller diameter than the upper or
free extremities ; and thus each has the form of a truncated cone,
rather than of a cylinder. (Fig. 22.) This is well seen in the cells
which cover the villi of the intestinal canal. (Fig. 28.) On the other
hand, where the cylinder-epithelium lies upon a concave surface, the
free extremities of the cells may be smaller than those which are
attached. Sometimes each cylinder is formed from more than one
cell, as is shown by the nuclei it contains ; although its cavity seems
to be continuous from end to end. And occasionally the cylinders
arise by stalk-like prolongations, from a tesselated epithelium beneath.
The two forms of Epithelium pass into one another at various points;
and various transitional forms are then seen, — the tesselated scales
appearing to rise more and more from the surface, until they project
as long-stalked cells, truncated cones, or cylinders.

234. Both these principal forms of Epithelial cells are frequently
observed to be fringed at their free margins with delicate filaments,

which are termed cilia; and these,
although of extreme minuteness, are
organs of great importance in the ani-
mal economy, through the extraordi-
nary motor powers with which they
are endowed. The form of the ciliary
filaments is usually a little flattened,
and tapering gradually from the base
to the point. Their size is extremely
variable ; the largest that have been
observed being about l-500th of an inch in length, and the smallest
about l-13,000th. When in motion, each filament appears to bend
from its root to its point, returning again to its original state, like the
stalks of corn when depressed by the wind ; and when a number are
affected in succession with this motion, the appearance of progressive
waves following one another is produced, as when a corn-field is
agitated by frequent gusts. When the ciliary motion is taking place
in full activity, however, nothing whatever can be distinguished, but
the whirl of particles in the surrounding fluid ; and it is only when
the rate of movement slackens, that the shape and size of the cilia,
and the manner in which their stroke is made, can be clearly seen.
The motion of the cilia is not only quite independent (in all the
higher animals at least) of the will of the animal, but is also inde-
pendent even of the life of the rest of the body ; being seen after the
death of the animal, and proceeding with perfect regularity in parts
separated from the body. Thus isolated epithelium-cells have been
seen to swim about actively in water, by the agency of their cilia, for
some hours atler they have been detached from the mucous surface
of the nose ; and the ciliary movement has been seen fifteen days
after death in the body of a Tortoise, in which putrefaction was far
advanced. In the gills of the River-Mussel, which are among the

Vibratile or ciliated Epithelium ;— a,
nucleated cells, resting on their smaller
extremities; b, cilia.

SIMPLE ISOLATED CELLS.— EPITHELIUM. 151

best objects for the study of it, the movement endures with similar
pertinacity.

235. The purpose of this ciliary movement is obviously to propel
fluids over the surface on which it takes place ; and it is consequently
limited in the higher animals to the internal surfaces of the body, and
always takes place in the direction of the outlets, towards which it
aids in propelling the various products of secretion. The case is
different, however, among animals of the lower classes, especially
those inhabiting the water. Thus the external surface of the gills of
Fishes, Tadpoles, &c., is furnished with cilia; the continual move-
ment of which renews the water in contact with them, and thus
promotes the aeration of the blood. In the lower Mollusca, and in
many Zoophytes, which pass their lives rooted to one spot, the motion
of the cilia serves not merely to produce currents for respiration, but
likewise to draw into the mouth the minute particles that serve as
food. And in the free-moving Animalcules, of various kinds, the
cilia are the sole instruments which they possess, not merely for pro-
ducing those currents in the water which may bring them the requisite
supply of air and food, but also for propelling their own bodies through
the water. This is the case, too, with many larger animals of the
class Acalepha (Jelly-fish), which move through the water, sometimes
with great activity, by the combined action of the vast numbers of
cilia that clothe the margins of their external surfaces. In these latter
cases it would seem as if the ciliary movement w^ere more under the
control of the will of the animal, than it is where it is concerned only
in the organic functions. In what way the will can influence it, how-
ever, it does not seem easy to say ; since the ciliated epithelium-cells
appear to be perfectly disconnected from the surface on which they
lie, and cannot, therefore, receive any direct influence from their
nerves. Of the cause of the movement of the cilia themselves, no
account can be given ; they are usually far too small to contain even
the minutest fibrillee of muscle ; and we must regard them as being,
like those fibrillse, organs sui generis, having their own peculiar en-
dowment,— which is, in the higher animals at least, that of continuing
in ceaseless vibration, during the whole term of the life of the cells
to which they are attached. The length of time during which the
ciliary movement continues after the general death of the body, is
much less in the warm-blooded than in the cold-blooded animals;
and in this respect it corresponds with the degree of persistence of
muscular irritability, and of other vital endowments.

236. The Tesselated-Epithelium, as already mentioned, covers the
Serous and Synovial membranes, the lining membrane of the blood-
vessels and absorbents, and the Mucous membranes with their glan-
dular prolongations, except where the cylinder-epithelium exists. It
presents itself, with some modifications presently to be noticed, in the
ultimate follicles of all glands, and also in the air-cells of the lungs.
In this latter situation it is furnished with cilia ; and these are also
found on the cells of the tesselated-epithelium, which covers the deli-

159 SIMPLE ISOLATED CELLS.—EPITHELIUM.

cate pia mater lining the cerebral cavities. — The Cylinder-Epithelium
commences at the cardiac orifice of the stomach, and lines the whole
intestinal tube; and, generally speaking, it lines the larger gland-
ducts, giving place to the tesselated form in their smaller ramifica-
tions. A similar epithelium, furnished with cilia, is found lining
the air-passages and their various offsets, — the nasal cavities, frontal
sinuses, maxillary antra, lachrymal ducts and sac, the posterior surface
of the pendulous velum of the palate and fauces, the Eustachian tubes,
the larynx, trachea, and bronchi, — becoming continuous, however,
in the finer divisions of the latter, with the ciliated pavement-epi-
thelium. The upper part of the vagini, the uterus, and the Fallopian
tubes, are also furnished with a ciliated Cylinder-epithelium. The
function of the cilia in all these cases appears to be the same ; that of
propelling the viscid secretions, which would otherwise accumulate
on these membranes, towards the exterior orifices, whence they may
be carried off*.

237. The simplest office which the Epithelium-cells of Mucous
membranes perform, appears to be that of elaborating a peculiar
secretion, termed Mucus; which is destined to protect them from the
contact of air, or from that of the various irritating substances to
which they are exposed, in consequence of their peculiar position and
functions. This Mucus is a transparent semi-fluid substance, dis-
tinguished by its peculiar tenacity or viscidity. It is quite insoluble
in water ; but is readily dissolved by dilute alkaline solutions, from
which it is precipitated again by the addition of an acid. A substance
resembling Mucus may be produced from any fibrinous exudation, or
even from pus, by treating it with a small quantity of liquor potassse.
The secretion of Mucus, like the formation of Epidermis, appears to
take place with an activity proportioned to the degree of irritation of
the subjacent membrane. On many parts of the mucous surface, a
sufficient supply is afforded by the epithelium-cells which cover it ;
but in other situations, especially along the alimentary canal, the
demand is much greater, and it is supplied not merely by the cells
of the surface, but by those lining the crypts or follicles which are
formed by involutions of it. There is reason to believe that the
whole epithelial covering of the stomach and intestinal tube (along
the upper part of the latter at least) is cast oft' at every meal (Fig. 27);
the cells growing from their germs, elaborating their mucous secretion,
and then bursting or liquefying to set this free, in the course of a few
hours. The debris of these secreting cells may be recognized in the
substances voided from the intestine ; as well as in the mucus taken
from the surface of any mucous membrane.

238. The Epithelium-cells, which are thus being continually re-
newed on the Mucous surfaces, commonly seem to have their origin
in the granular germs diffused through the basement-membrane ; but
it is different in regard to the cells of the follicles, which seem rather
to occupy their cavity than merely to line their walls, and which
appear to be in course of continual production from a germinal spot,

SIMPLE ISOLATED CELLS.— SECRETING CELLS. 153

or collection of reproductive granules, at the blind extremity of the
follicle. This is the case in the ultimate follicles of the more complex
glands; which may be regarded as so many repetitions of the simple
crypts or follicles in the substance of the mucous membranes ; — the
only difference being, that the former pour their secretion into a
branch of a duct, which unites with the other ramifications to form
a trunk ; and this trunk conveys them to their destination in some
cavity lined by a mucous membrane ; — whilst the simple follicles or
crypts at once pour forth their secretions upon the surface of the
membrane. The accompanying figure represents two follicles of the

Fig. 23. Fig 24.

Two follicles from the liver of Carcmt« Ultimate follicles of Mammary

mcBnas, (Common Crab), with their con- gland, with their secreting cells, a,

tained secreting cells. «;— *, b, the nuclei.

liver of the Common Crab, which are seen to be filled with secreting
cells ; it is evident, from the comparative sizes of these cells in dif-
ferent parts, that they originate at the blind extremity of the follicle,
where there is a germinal spot; and that, as they recede from that
spot, they gradually increase in size, and become filled wath their
characteristic secretion, being at the same time pushed onwards
towards the outlet by the continual new growth of cells at the ger-
minal spot. In Fig. 24 are shown the corresponding ultimate folli-
cles of the Mammary gland ; filled, like the preceding, wuth secreting
cells.

239. The whole of the acts, then, by which the separation of the
different Secretions from the Circulating fluid is accomplished, really
consist in the growth and nutrition of a certain set of cells, usually
covering the free surfaces of the body, both internal and external, or
lining cavities which have a ready communication with these by
means of ducts or canals.* These cells differ widely from one an-
other, in regard to the kind of matter which they appropriate and
assemble in their cavities; although the nature of their walls is pro-
bably the same throughout. Thus we find biliary matter and oil,
easily recognizable by their colour and refracting power, in the cells
of the liver; milk in the cells of the mammary gland ; sebaceous or
fatty matter in the cells of the sebaceous follicles of the skin ; and so
on. All these substances are derived from the blood ; being either
contained in it previously, or being elaborated from its constituents

* The Synovial secretion is, perhaps, the only one which is poured into a closed
sac.

154

SIMPLE ISOLATED CELLS^-REPRODUCTIVE CELLS.

by a simple process of transformation, — as, for exam]5le, that which
converts the albumen of the blood into the casein of milk. Hence
they may be considered as the peculiar aliments of the several groups
of cells ; whose acts of nutrition are the means of drawing them off
or secreting them, from the general circulating fluid.
When they have attained their full growth, and ac-
complished their term of life, their walls either burst
or dissolve away, and thus the contents of the cells
are delivered into the cavity, or upon the surface, at
which they are required. Now as all the canals of
the glands open either directly outwards upon the

Fig. 25.

Secreting cells of
Human Liver; a, nu-
cleus; ft, nucleolus; c,
oil-particles.

surface, or into cavities which communicate with

the exterior, it is evident that the various products
of the action of these epithelial cells must be destined
to be cast forth from the body. This we shall find to be the case ;
some of them, as the bile and urine, being excretions, of which it is
necessary to get rid by the most direct channel ; whilst others, like
the tears, the saliva, the gastric fluid, the milk, &c., are separated
from the blood, not so much for its purification, but because they are
required to answer certain purposes in the economy.

240. Now whilst thus actively concerned in the Nutritive functions
of the economy, and exercising in the highest degree their powers of
selection and transformation, these Secreting cells appear to have
nothing to do with the operation of Reproduction. We have seen
that they do not even regenerate themselves ; all their energies being,
as it were, concentrated upon their own growth ; and the successive
production of new generations being provided for by other means.
But special Reproductive cells, destined to furnish the germs for the
continuance of the race, are not wanting. These are developed

within the tubuli of the Testicle ; where
they appear to hold exactly the same
relation to the membranous walls of
those tubuli, as do the secreting cells
to the tubes and follicles of the proper
Glands. The contents of these repro-
ductive cells are peculiarly granular;
and the granules are at one time dif-
fused through the entire cell. They
are afterwards seen, however, to pre-
sent a regular linear arrangement ;
forming a bundle of fibrous bodies, still
comprehended, however, within the
cell. After a time, however, the con-
taining cells burst, and the fibrous
bodies within separate and are set free.
From the very peculiar motion which they possess, they were long
regarded as distinct Animalcules, and received the designation of
Spermatozoa. It is now generally admitted, however, that they have

Fig. 26.

Formation of Spermatozoa within semi-
nal cells ; a. the original nucleated cell ; 6,
the same enlarged, with the formation of
the Spermatozoa in progress ; c, the Sper-
matozoa nearly complete, but still enclosed
within the cell.

SIMPLE ISOLATED CELLS.— ABSORBENT CELLS. 155

no more claim to a distinct animal character, than have the ciliated
epithelia of mucous membrane, which will likewise continue in move-
ment when separated from the body. The so-called Spermatozoa
appear to be nothing else than cell-germs, furnished with a peculiar
power of movement, by means of which they are enabled to make
their way into the situation where they may be received, cherished,
and developed, — as will be shown hereafter. (Chap. XT.) It is a
curious fact that the seminal cells, in which the Spermatozoa are
formed, are sometimes ejected from the gland, not only before they
have burst and set free the Spermatozoa, but even long before the
development of the Spermatozoa in their interior is completed; — thus
affording a complete demonstration of their independent vitality.

241. We now proceed to a class of cells, which are equally
independent of each other, which begin and end their lives as cells,
without undergoing any transformation, but which form part of the
substance of the fabric, instead of lying upon its free surfaces and
being continually cast off from them. Still their individual history is
much the same as that of the cells already noticed ; and they differ
chiefly in regard to the destination of their products. — The first group
of this class deserving a separate notice, is that which effects the
introduction of aliment into the body; — of those kinds of aliment, at
least, which are not received in solution by any more direct means.
Along the greater part of the intestinal tube, from the point at which
the hepatic and pancreatic ducts enter it, to the rectum, we find the
mucous membrane furnished with a vast number of minute tufts or
folds, by which its free surface is vastly extended ; these are termed
villi. They may be compared to the ultimate root-fibres of trees, both
in structure and function ; for each of them gives origin to a minute
lacteal or chyle-absorbing vessel, which occupies its centre ; whilst
it also contains a copious network of blood-vessels, (Fig. 8, p. 118,)
which appears likewise to participate in the act of absorption, by
taking up substances that are in complete solution. Now at the end
of every villus, there may be seen, whilst the process of digestion
and absorption is going on, a cluster of minute cells, in the midst of
which the origin of the lacteal is lost. These cells, whose size varies
from 1-lOOOth to l-2000th of an inch, are turgid with a milky fluid,
which is evidently the same with that which is found in the lacteals ;
and there is good reason to believe, that it is by the growth and
nutrition of these cells, that this milky fluid, the chyle, is selected
from the contents of the digestive cavity. Their function, therefore, is
precisely the converse of that of the secreting cells already described;
whilst the history of their individual lives is the same. These absor-
bent cells draw their materials from the fluid in the digestive cavity,
instead of from the blood ; and when they burst or liquefy, they set
free their contents where they may be taken up by a lacteal and con-
veyed into the circulating current, instead of pouring them into a
cavity through which they will be shortly expelled.

242. In the intervals of the digestive process, the extremities of the

156

ABSORBENT CELLS.

villi are comparatively flaccid ; and instead of cells, they show merely
a collection of granular germs. These begin to develop themselves,
as soon as the food has been dissolved in the stomach and transmitted
to the intestine; and their development goes on, as long as the villi
are surrounded with nutrient matter. The cells rapidly grow, select,
absorb, and prepare the nutritious matter, by making it a part of
themselves; and, when their work is accomplished, they deliver it to
the lacteals by their own rupture or deliquescence. The accompany-
ing diagrams represent the comparative condition of the Mucous

Fig. 27.

Diagram of mucous membrane during diges-
tion and absorption of chyle; a, a villus, turgid
and erect; its protective epithelium cast off from
its free extremity; its absorbent vesicles, its lac-
teals, and its blood-vessels turbid ; b, a follicle
discharging its secreting epithelial cells.

Diagram of mucous membrane of jejunum,
when Absorption is not going on ; a, protec-
tive epithelium of a villus; &, secreting epi-
thelium of a follicle ; c, c, c, primary membrane,
■with its germinal spots or nuclei, d, d; e,
germs of absorbent vesicles;/, vessels and
lacteals of villus.

membrane, its villi, and its secreting follicles, during the time when
absorption is going on, and in the intervals of the process. It will
be seen that, in the former state, the epithelium-cells are not only
being cast off from the free surface of the membrane, and from the
interior of the follicles ; but they are also detached from the surface
of the villus, that they may offer no impediment to the process of
absorption. During the intervals of digestion, the secreting epithe-
lium of the follicles, and the protective epithelium of the villi, are
alike renewed, from the germs supplied by the basement-membrane.
243. Although the mucous membrane of the intestinal tube is the
only channel through which insoluble nutriment can be absorbed in
the completely-formed Mammal, and the only situation, therefore, in
which w^e meet with these absorbent cells, there are other situations
in which similar cells perform analogous duties in the embryo. Thus
the Chick derives its nutriment, whilst in the egg, from the substance
of the yelk, by absorption through the blood-vessels spread out in the
vascular layer of the germinal membrane surrounding the yelk ; which
vessels answer to the blood-vessels and lacteals of the permanent
digestive cavity, and are raised into folds or villi as the contents of
the yelk-bag are diminished. Now the ends of the vessels are sepa-
rated from the fluid contents of the yelk-bag, by a layer of cells ;

ABSORBENT CELLS.

157

which seems to have for its object to select and prepare the materials
supplied by the yelk, for being received into the absorbent vessels.

244. In like manner, the embryo of the Mammal is nourished, up
to the time of its birth, through the medium of its umbilical vessels ;
the ramifications of which form tufts, that dip down, as it were, into
the maternal blood, and receive from it the materials destined to the
nutrition of the foetus; besides effecting the aeration of the blood of
the latter, by exposing it to the more oxygenated blood of the mother.
Now around the capillary loop of the fcetal tuft, there is a layer of
cells, closely resembling the absorbent cells of the villi ; and these
are enclosed in a cap of basement-membrane, which completes the
foetal portion of the tuft, and renders it comparable in all essential
respects to the intestinal villus. It is again surrounded, however, by
another layer of membrane and of cells, belonging to the maternal
system ; — the derivation and arrangement of which will be explained
hereafter. The maternal cells (6, Fig. 29) may be regarded as the

Fig. 29.

Extremity of a placental villus:— a, external membrane of the
villus, continuous with the lining membrane of the vascular system
of the mother; b, external cells of the villus, belonging to the pla-
cental decidua ; c, c, germinal centres of the external cells ; d, the
space between the maternal and fecial portions of the villus; e, the
internal membrane of the villus, continuous with the external
membrane of the chorion;/, the internal cells of the villus, belong-
ing to the chorion; g, tlie loop of umbilical vessels.

first selectors of nutriment from the circulating fluid of the parent: the
materials, partially prepared by them, are poured into the cavity (d)
surrounding the extremity of the tuft; and from this they are taken
up by the foetal cells {/), which further elaborate them, and impart
them to the capillary loop (g) of the umbilical vessels.

245. Thus we see that the several functions of Selection, Absorp-
tion, Assimilation, Respiration, Secretion, and Reproduction, are
performed by the agency of cells in the Animal as in the Vegetable
kingdom, — in the complex Human organism, as in the humblest
Cryptogamic Plant ; the only difference being, that in the latter there
is a greater division of labour, different groups of cells being appro-
priated to different functions, in the general economy, whilst the
history of their own processes of nutrition and decay is everywhere
essentially the same. Thus we have seen that the Absorbent cells, at
the extremities of the intestinal or placental villi, select and draw into
themselves, as the materials of their own growth, certain substances
in their neighbourhood ; which are still as much external to the tissues
of the body, as are the fluids surrounding the roots of plants. Having
come to their full term of life, they burst or dissolve away, and give
up their contents to the absorbent vessels, which carry them into the
general current of the circulation, where they are mingled with the
fluid previously assimilated, — the blood. Whilst passing through the
vessels, they are subjected to the action of another set of cells, (the

158 SIMPLE ISOLATED CELLS.

lymph and cbyle-corpuscles, and the colourless corpuscles of the
blood,) by which they are gradually assimilated, or converted into a
substance of a more directly organizable character ; these assimilating
cells being developed from germs that float in the fluid, drawing into
themselves the albuminous matter, converting it into fibrin, and then
setting it free by their own dissolution. In the same fluid another
set of cells, the red corpuscles of the blood, are observed to float, in
the higher classes of animals ; whose special function appears to be
the conveyance of oxygen from the lungs to the tissues, and of car-
bonic acid from the tissues to the lungs; in other words, that of
Respiration: these cells do not appear to pass through their course of
existence as rapidly as the preceding. Next we have various groups
of cells, external to the vessels, on the free surfaces of the body;
whose oflSce it is to draw from the blood certain materials, which are
destined for Secretion or separation from it ; either for the sake of
preserving that fluid in its requisite purity, or for answering some
other purpose in the system. These cells grow at the expense of the
substances, w^hich they draw into themselves from the blood ; and on
their dissolution, they cast forth their contents on the free surfaces
communicating with the exterior of the body, to which they are in
time conveyed. And, lastly, we have a special set of cells, destined
to prepare the germs of new beings ; which are, in like manner, set
free by the rupture of the parent-cell, in a condition that enables
them to be conveyed to a place appropriated for their further develop-
ment, and thus to perform the essential part of the process of Repro-
duction.

246. The cells which are thus the active instruments of the Organic
functions, are produced and succeed one another with a rapidity pro-
portional to the energy of those functions. The causes which influence
their growth and decay are not always evident; thus we occasionally
find an extraordinary tendency to the elaboration of Fibrin, as mani-
fested in the increase in the proportion of that ingredient of the blood,
and in the number of the Assimilating cells or white corpuscles that
float in that fluid ; and as to the causes of this condition, which is one
important part of the disordered state termed Inflammation, we are
almost entirely in the dark. The development of the Absorbent cells
appears to depend upon the supply of alimentary materials afforded
by the contents of the digestive cavity ; and also upon the supply of
blood furnished by the capillaries of the villi, from which last the
materials of the cell-walls are probably derived. The conditions of
the development of the Secreting cells are not sufficiently understood ;
it does not appear to depend solely upon the supply of their materials ;
for, as we shall see hereafter, these materials may accumulate unduly
in the blood, through the insufficient production of the cells which
are destined to separate them ; whilst, on the other hand, the presence
of certain substances in the blood appears to accelerate their develop-
ment. Of these stimuli. Mercury is one of the most powerful ; and
we have continual opp©rtuniti€s of witnessing its effects, in giving an

CELLS CONNECTED TOGETHER IN SOLID TISSUES. 159

increased activity to the secreting actions. There is probably not a
gland in the body, which is not in some degree influenced by its pre-
sence in the blood ; but the liver, the kidneys, the salivary glands,
and the glandulae of the intestinal canal, appear to be those most
affected by its stimulating powers. The action of the glands, in other
words the development of the secreting cells, appears to be influenced
by mental emotions ; being sometimes accelerated, and sometimes
retarded, through their agency. This is especially the case in regard
to the secretion of Milk, Tears, Saliva, and Gastric juice. But we
shall hereafter see that the influence thus manifested is probably
exerted through the capillary circulation, which is known to be power-
fully affected by mental emotions, as in the acts of blushing and erec-
tion ; and that the increased production of the secretion is immediately
due to the increased flow of blood to the gland. We have an example
of this, in the " draught" (as it is termed) experienced by Nurses,
when the child is applied to the breast ; which is a perceptible rush
of blood into the organ.

5. Of Cells connected together as permanent constituents of the Tissues.

247. We now pass on to consider those Cells which enter as com-
ponent elements into the solid and permanent fabric of the body, and
which do not take so active a part in its vital operations. These we
shall find to be usually more or less closely connected together, either
by a general enveloping membrane, or by an intercellular substance,
which is interposed between their walls, and holds them together by
its adhesive properties. Before entering upon the description of the
tissues thus formed, it will be desirable to consider a little more fully
the mode in which the component cells are developed, and the cha-
racter of the transformations they may undergo.

248. We have seen that a minute isolated molecule, prepared by a
parent-cell, and set free by its dissolution, may become the germ of a
new cell ; and that the assimilating cells which float in the animal fluids
seem to have their origin, like the equally-simple cells of the Yeast-
fungus, in such floating germs ; whilst the epithelial and epidermic
tissues arise from similar granules diffused through the substance of
the basement-membrane, or aggregated in its germinal spots. But the
usual mode of development of the cells of a higher and more perma-
nent character, is somewhat different ; for these are developed within
the parent-cell, which, instead of dissolving away, may remain as a
thin membrane around them ; — all traces of it, however, at last
disappearing, in consequence of the distension which it undergoes.
Even whilst still evidently contained within the parent-cell, the
secondary cells may themselves be developing a third generation
within them. The rapidity of the process, and th« number of cells
thus developed, appear to bear a close relation with the transitory or
permanent character of the structure. It is in Cancerous growths,
that we meet with the most remarkable examples of rapid production ;

160

CELLS CONNECTED TOGETHER IN SOLID TISSUES.

Fig. 30.

Parent-cells, a, a, of cancer-
ous structure, containing se-
condary cells, b, b, each having
one, two, or three nuclei, c, c.

a large number of secondary cells being developed within each pri-
mary ; these secondary cells again becoming the parents, each one of
an equally large generation ; and so on. Here
the whole energy seems concentrated upon
the reproductive process ; and we find that
growths composed of such cells have a very
rapid increase, but very little solidity or per-
manence.— On the other hand we find that,
in structures which are destined to undergo
a higher development, and to possess a more
permanent character, the number of cells
developed within each parent is more limit-
ed ; thus in the early development of the
embryo of Mammalia it is limited to two;
and the first pair of cells is thus progressively
developed into four, eight, sixteen, and so
on. The same tendency to a binary multiplication is apparent also
in the cells of Cartilage (§ 267) ; and it probably exists also in other
cellular structures of a permanent character.

249. It is most coipmonly to be observed in these cells, that the
reproductive granules, instead of being diffused throughout the cavity
of the cell, — as they are in the cells of the Cryptogamic Plants, the
White Corpuscles of the blood of Animals, &c. &c., — are concen-
trated in one spot, forming a nucleus (Figs. 20, 21); and it is from
this nucleus that the new cells originate. The granules appear to
undergo the same changes, when developed in this situation, as they
do when isolated within the cell, or altogether set free ; at first they
show a simple enlargement, looking like little warts projecting into
the cell ; this enlargement continues, until the difference between the
cell-wall and the cavity, the containing and the contained parts,
becomes perceptible ; and the character of the young cell is then
obvious.

250. According to Dr. Barry's observations on the processes of
cell-growth in the germinal vesicle and early embryo of the Rabbit,
it is the outer circle of granules forming the nucleus, which is first
developed into young cells ; the next then commences, and pushes
outwards the ring of cells previously formed; and by the continuance
of the same process, the parent-cell may be completely filled with a
new generation. Of these, however, the greater part may be destined
to liquefy or dissolve away; their office having apparently been, to
assimilate or prepare the materials that are destined for the nutrition
of the permanent ofispring, which are the cells latest formed in the
centre of the nucleus. A pellucid spot, which is frequently seen in
the centre of the nucleus, has received the name of nucleolus (Fig.
20, c); sometimes two or even three nucleoli may be seen in a single
nucleus (Fig. 21, a). The cause of this appearance is not precisely
understood ; but it seems to be of a transitory character, indicating a
certain stage in the conversion of the nucleus into new cells.

CELLS CONNECTED TOGETHER IN SOLID TISSUES. 161

251. The function of the nucleus in the development of new cells,
is thus evidently identical with that of the " germinal spots" already
described as existing at the extremity of the secreting follicles (§ 238),
or in the substance of the basement-membrane. In fact'we are pro-
bably to regard each secreting follicle as a large parent-cell ; of which
the functions are permanent, instead of transitory ; and which, having
opened into a neighbouring duct, instead of remaining closed, con-
tinues to develop new secondary or secreting cells, from the nucleus
or germinal spot at its opposite extremity, to an unlimited extent.
And it is probable, also, that the " germinal spots" in the substance of
the basement-membrane are really the nuclei of cells, by the coales-
cence of which it is formed, in the manner to be presently noticed.

252. Now if the walls of the parent-cells, instead of liquefying or
thinning away, are thickened or strengthened by additional nutrition,
they may remain as permanent vesicles, enclosing and holding together
numerous secondary cells; and this appears to be the case in Adipose
tissue, and also in tumours of various kinds.

253. Where such enveloping membranes are wanting, we fre-
quently find the component cells of the permanent tissues of Animals
(Rke those of the higher plants) held together by an intercellular sub-
stance ; which generally presents no distinct traces of organization ;
and which usually consists of Gelatin, or of a substance allied to it in
composition. The proportion of this substance to the cells may vary
in different cases ; and very different characters may thus be presented
by a tissue made up of the same elements. Thus the subjoined figure
represents a portion of one of the animal layers included between the
calcareous laminse of a bivalve shell ; in which we see on the one side
a number of nuclei or incipient cells, scattered through a bed of homo-
geneous intercellular substance, and bearing but a very small propor-
tion to it; whilst the opposite end exhibits a set of polygonal cells, in
close contact with each other, the intercellular substance being only
represented by the thick dark lines, which mark the boundaries of the
cells, and which are rather thicker at the angles of the latter. Between
these two extremes, we observe every stage of transition.

254. The presence of a very large amount of intercellular substance,
through which minute cells are scattered at considerable intervals,
(Fig. 31, a,) is characteristic of various forms of Cartilage; and more
particularly of that soft semi-cartilaginous structure, of which the
Jelly-fish are for the most part composed. In other forms of cartilage,
we find the cells more developed, and in closer proximity to each
other, the proportion of the intercellular substance being at the same
time diminished (as seen at h and c. Fig. 31) ; but it is not often,
save in embryonic structures, that we find the cells in such close
proximity, and the intercellular substance so nearly wanting, as at d.
Such examples do occasionally present themselves, however, even in
the soft tissues. Thus the chorda dorsalis, which replaces the verte-
bral column in the lowest Fishes, and of which the analogue is found
in the embryos of the higher Vertebrata, is made up of a structure of

162

CELLS CONNECTED TOGETHER IN SOLID TISSUES.

this kind. The true Skin, in the Short Sun-fish, is replaced by a
similar layer of cellular tissue, which extends over the whole body,
varying in thickness from one-fourth of an inch to six inches. And

Fig. 31.

Portion of shell-membrane, showing theorigin of cells in the midst of horny intercellular substance;
a, nuclei; b, incipient cells; c, the same further advanced, but separated by intercellular substance
d, the cells become polygonal by mutual pressure.

in the Lancelot (a little fish which is destitute of so many of the
characters of a Vertebrated animal, that its right to a place in that
division has been doubted), a considerable portion of the fabric is
made up of a similar parenchyma.

255. Now we shall find that one method, by which the requisite
firmness and solidity are given to the animal fabric, consists in the
deposition of earthy substances in the interior of such cells, by a peculiar
secreting action of their own. Thus in Shell, we find them completely
filled up with carbonate of lime ; and in Bones and Teeth with car-
bonate and phosphate of lime. When this is the case, there is a
tendency to an apparent coalescence of the cells, by the obliteration of
their partitions ; or rather, perhaps, by the removal of the whole
intercellular substance from between them, the actual cell-walls being
so very thin, that they are not distinguishable. The incipient stages
of this coalescence, as seen in another portion of the same membrane
as that represented in the last figure, are shown in Fig. 32. At a.

Fig. 32.

Portion of shell-membrane, showing the gradual coalescence of distinct cells ; at a, the cells sepa-
rated by iatercellular substance ; at 6, the partitions are thinner ; and at c, they almost disappear.

COALESCENCE AND METAMORPHOSIS OF CELLS. 163

the nucleated cells are very distinct; and are separated by a large
quantity of intercellular substance. At b, they approach each other
more closely, the amount of intercellular substance being less ; the
widest intervals are seen at the angles of the cells. At c, the approxi-
mation is much closer ; and the cell-walls are scarcely distinguishable
at the points where they come into immediate contact. Proceeding
further, we observe that the partitions are much less complete ; so
that the originally distinct cellular character of the membrane is chiefly
indicated by the bright nuclei, which are regularly dispersed through
it, and by the triangular dark spots, which show the remains of the
intercellular substance at the angles where three cells join each other.
The coalescence may be traced further than it is shown to do in the
figure ; so that, if it were not for the evidence afforded by the transi-
tion-stages here represented, it would be difficult to prove that the
membranous layer had its origin in cells.

256. These facts, respecting the gradual coalescence of cells, ex-
plain not merely the appearances presented in Tooth, Shell, &c.
(hereafter to be described) ; but also those which are exhibited by
the Basement-membrane, as already detailed (§ 206.)

257. There is no evidence, in the preceding case, that the cavities
of the cells coalesce ; and there is no reason why they should do so.
But we often find such an union, where the production of a continuous
tube is required. The long straight open ducts, through which the sap
of Plants rises in the stem, are unquestionably formed by a coalescence
of the cavities of cells of a cylindrical form, placed regularly end to
end ; and it seems probable that the network of anastomosing vessels,
through which the elaborated sap finds its way to the various parts of
the vegetable fabric, is formed, in like manner, by the coalescence of
cells, arranged obliquely and transversely in regard to one another.
In like manner, the capillary Blood-vessels of Animals are usually
believed to originate in rows of cells, the cavities of which have run
together by the obliteration of the transverse partitions ; as the per-
sistent nuclei of such cells may be occasionally brought into view in
the walls of the capillaries. And the same appears to be the origin
of the tubular fibres of Muscular and Nervous tissue, which contain
the elements characteristic of those tissues; these elements, — the
fibrillae of muscle, and the granular pith of the nerve-tube, — being
evidently the secondary products of parent-cells, which seem to remain
as their investing tubuli, in the walls of which the original nuclei are
often to be seen (§§ 338 and 388).

258. Besides these changes, the original cells may often undergo
marked alterations of form; and this quite independently of any pres-
sure to which they may be subject. Thus the pigment-cells, as
already mentioned (§ 229,) frequently exhibit a curious stellate form;
arising from the development of radiating prolongations, which are
put forth from the original spheroid. A form which is frequently
assumed by the cells that are developed in fibrinous or plastic exu-
dations, and which is also met with in the cells of tumours, both

164

FUSIFORM CELLS.—ADIPOSE TISSUE.

malignant (or Cancerous) and non-malignant, is that which has re-
ceived the designation oi fusiform or spindle-like, from its prolonged
shape and pointed extremities. The various stages of transition,
which may be observed between the simple rounded cell and the
fusiform cell, are shown in Fig. 33 ; and it is there seen that, when
the transformation has gone to its utmost extent, the nucleus of the
cell is no longer visible, so that it bears a close resemblance to a
simple fibre. Such cells are found amongst the simple fibrous tissues ;
and, in the opinion of many, they give origin to them. — The appear-
ance of tissue, composed of fusiform cells, is shown in Fig. 34; this is
seldom met with as a permanent part of the normal fabric ; but it is a
frequent product of morbid action.

Fig. 33.

Fig. 35.

Fusiform tissue of plastic
exudations; o, fusiform bo-
dies without nuclei ; b, nu-
cleated fusiform cells ; c,
granular intercellular sub-
stance.

Areolar and Adipose tissue ;
a, a, fat-cells; 6, 6, fibres of are-

Transition from cellular to
fusiform tissue ; a, circular or
oval cells; 6, the siime becoming
pointed; c, fusiform cells con-
taining nuclei ; rf, fusiform cells
more elongated, and destitute
of nuclei.

259. We now proceed with the description of the various tissues
in the Human body, which are composed of cells united or trans-
formed in the foregoing manner ; and we shall commence with Adipose
or Fatty tissue, which may be considered as a sort of link, connect-
ing the permanent tissues with those which are more actively con-
cerned in the processes of Nutrition, Secretion, &c. The Adipose
tissue is composed of isolated cells, which have the power of appro-
priating fatty matter from the blood, precisely in the same manner as
the secreting cells appropriate the elements of bile, milk, &c. These
cells are sometimes dispersed in the interspaces of the Areolar tissue ;
whilst in other cases they are aggregated in distinct masses, — consti-
tuting the proper Adipose tissue. In the former case they are held in
their places by fibres, that traverse the areolae in different directions ;
whilst in the latter, each small cluster of fat cells is included in a
common envelop, on the exterior of which the blood-vessels ramify;
and these sacculi are held together by areolar tissue. We are thus
probably to regard each fatty mass in the light of a gland, or assem-

I

ADIPOSE TISSUE. 165

blage of secreting cells, penetrated by blood-vessels, and bound
together by fibrous tissue ; but having its follicles closed instead of
open, (which, as just now stated, appears to be the early conditions
of the follicles of all glands, § 251 ;) and consequently retaining its
secretion within itself, instead of pouring it forth into a channel for
excretion.

260. The individual fat-cells always present a nearly spherical or
spheroidal form ; sometimes, however, when they are closely pressed
together, they become somewhat polyhedral, from the flattening of
their walls against each other. Their intervals are traversed by a
minute network of blood-vessels, from

which they derive their secretion ; and it ^^g- ^^-

is probably by the constant moistening of

their walls with a watery fluid, that their

contents are retained without the least

transudation, although they are quite fluid

at the temperature of the living body. If

the watery fluid of the cell- walls of a mass

of Fat be allowed to dry up, and it be kept

at a temperature of 100°, the escape of Capillary network around Fat-cells.

the contained oily matter is soon percep-
tible.— By this provision, the fatty matter is altogether prevented
from escaping from the cells of the living tissues, by gravitation or
pressure ; and as it is not itself liable to undergo change when secluded
from the air, it may remain stored up, apparently unaltered, for an
almost unlimited period.

261. The consistency, as well as the Chemical constitution, of the
fatty matter contained in the Adipose cells, varies in different animals,
according to the relative proportions of three component substances,
which may be distinguished in it, — Stearine, Margarine, and Oleine.
The two former are solid when isolated, and the latter is fluid; but
at the ordinary temperature of the warm-blooded animal, they are
dissolved in it. Of these, Stearine is the most solid ; and it is most
largely present, therefore, in the hardest fatty matter, such as mutton^
suet. It is crystaline like spermaceti ; it is not at all greasy between
the fingers, and it melts at 143°. It is insoluble in water, and in
cold alcohol and ether ; but it dissolves in boiling alcohol or ether,
crystalizing as it cools. The substance termed Margarine exists
along with stearine in most fats; but it is the principal solid con-
stituent of Human fat, and also of Olive oil. It corresponds with
Stearine in many of its properties, and is nearly allied to it in Chemi-
cal composition ; but it is much more soluble in alcohol and ether,
and it melts at 118°. On the other hand, Oleine^ when pure, remains
fluid at the zero of Fahrenheit's thermometer; and it is soluble in
cold ether, from which it can only be separated by the evaporation
of the latter. It exists in small quantity in the various solid fats ; but
it constitutes the great mass of the liquid fixed oils. The tendency
of these to solidification by cold, depends upon the proportion of

166 ADIPOSE TISSUE.

stearine or margarine they may contain. All these substances are
neutral compounds, formed by the union of Stearic, Margaric, and
Oleic acids, respectively, with a base termed Glycerine; this base may
be obtained from any fatty matter, by treating it with an alkali, which
unites with the acid and forms a soap, setting free the Glycerine.
They contain no Nitrogen ; and their proportion of Oxygen is ex-
tremely small in regard to their amount of the Carbon and Hydrogen :
thus Stearine has 142 Carbon and 141 Hydrogen to 17 Oxygen ; and
in the other substances the proportions are similar. The fatty bodies
appear to be mutually convertible ; thus margaric acid may be pro-
cured from stearic acid, by subjecting it to dry distillation; and there
is ample evidence that animals supplied with one of them may pro-
duce the others from it.

262. Since these fatty matters are abundantly supplied by the
Vegetable kingdom, and are found to exist largely in substances which
were not previously supposed to contain them, it is not requisite to
suppose, that Animals usually elaborate them by any transforming
process from the elements of their ordinary food. The mode in which
they are taken into the blood, and the uses to which they are subserv-
ient, will be hereafter investigated ; but it may be here remarked,
that the portion separated from the circulating fluid to form the Adi-
pose tissue, is only that which can be spared from the other purposes,
to which the fatty matters have to be applied. Hence the production
of this tissue depends in part upon the amount of Fatty matter taken
in as food ; but this is not entirely the case, as some have main-
tained ; for there is sufficient evidence that animals may produce fatty
matter by a process of chemical transformation, from the starch or
sugar of their food, when there is an unusual deficiency of it in their
aliment.

263. The development of Adipose tissue in the body appears to
answer several distinct purposes. It fills up interstices, and forms
a kind of pad or cushion for the support of movable parts ; and so
necessary does it seem for this purpose, that, even in cases of great
emaciation, some fat is always found to remain, especially at the base
of the heart around the origin of the great vessels, and in the orbit of
the eye. It also assists in the retention of the animal temperature by
its non-conducting power ; and we accordingly find a thick layer of
it, in those warm-blooded mammals that inhabit the seas, — either
immediately beneath their skin, or incorporated with its substance.
And it also serves as a reservoir of combustible matter, at the expense
of which the respiration may be maintained when other materials are
deficient; thus we find that the respiration of hybernating animals is
kept up, during the period when they cease taking food (§ 121), by
the consumption of the store of fat which was laid up in their bodies,
previously to their passing into that state; and it is also to be noticed
that herbivorous animals, whose food is scanty during the winter,
usually exhibit a strong tendency to such an accumulation, during the
latter part of the summer, when their food is most rich and abundant,

ADIPOSE TISSUE.— CARTILAGE. 167

in order to supply the increased demand created by the low external
temperature of the winter season. Other circumstances being the
same, it appears that the length of time during w^hich a warm-blooded
animal can live without food, depends upon the quantity of fat in its
body ; for the rapid low^ering of its temperature, which is the imme-
diate cause of its death (§ 117,) takes place as soon as the whole of
this store has been exhausted. Of the means by which the fatty
secretion is taken back again into the current of the circulation, when
it is required for use in the system, we know nothing whatever.

264. In the simpler forms of Cartilage^ we have an example of a
tissue of remarkable permanence, composed entirely of cells scattered
through an intercellular substance. This substance has a close
resemblance to Gelatin, in composition and properties ; but is not
identical with it ; and has received the distinguishing appellation of
Chondrine, which marks it as the solidifying ingredient of Cartilage.
It requires longer boiling than Gelatin for its solution in water ; but
the solution fixes into a jelly in cooling, and dries by evaporation into
a glue that cannot be distinguished from that of gelatin. Chondrine
is not precipitated, however, by tannic acid, but, on the other hand,
it gives precipitates with acetic acid, alum, acetate of lead, and proto-
sulphate of iron, which do not disturb a solution of gelatin. That the
Chondrine obtained by boiling cartilage is an actual component of
that tissue, and is not a product of the operation, appears from the
fact that its elementary composition agrees with that of pure cartilage,
when analyzed by combustion. According to Mulder, the propor-
tions of the elements are as follows: 32 Carbon, 26 Hydrogen, 4
Nitrogen, 14 Oxygen ; with which one-tenth of an equivalent of sul-
phur is combined. This formula is deduced from the definite com-
pound which Chondrine forms w^ith Chlorine.

265. Now it is a very curious fact, that all the Cartilages of the
foetus, — those which are to be converted into bone, as well as those
which are to remain unossified, — are composed of Chondrine ; and
yet, as soon as the process of ossification commences, the chondrine
is replaced by gelatin, which is the sole organic constituent of the
intercellular substance of bones. The permanent cartilages, however,
still contain only Chondrine ; but if accidental bony deposits should
take place in them, (as frequently happens in old persons, especially
in the cartilages of the ribs,) the Chondrine gives place to Gelatin.
There can be little doubt that, in these cases, there is an actual con-
version of the Chondrine into Gelatin ; but the mode in which this is
effected, is not in the least understood. As Chondrine agrees more
nearly with Proteine, in its elementary composition, than Gelatin
does, it may be surmised that it is a sort of intermediate stage in the
conversion of Proteine into Gelatin ; but it must be kept in mind,
that no such substance is met wdth in any other of the gelatinous
tissues, — Chondrine being restricted to pure cellular cartilage. Those
in which the intercellular substance has the characters of the white
fibrous tissue (§ 189), yield gelatin on boiling, in the manner of the

168 CARTILAGE.

ligaments and tendons ; whilst those which contain much of the yel-
low or elastic tissue, undergo very little change by boiling, and only
yield, after several days, a small quantity of an extract which does
not form a jelly, but which has the other chemical properties of
Chondrine.

266. Besides the organic compounds already described, most Car-
tilages contain a certain amount of mineral matter, which forms an
ash when they are calcined. This ash contains a large proportion of
carbonate and sulphate of soda, together with carbonate of lime, and
a small quantity of phosphate of lime ; as age advances, the propor-
tion of the soluble compounds diminishes, and the phosphate of lime
predominates. This is especially the case in the costal cartilages,
which almost invariably become converted into a semi-ossified sub-
stance, in old persons ; and it is remarkable that, even before they
have themselves become thus condensed, they are united by ossific
matter, when they have undergone fracture.

267. When a pure Cellular Cartilage is examined microscopically,
its cells are seen to lie, sometimes singly, and sometimes in clusters
of two, three, or four, in cavities excavated in the intercellular sub-
stance ; and these occur at very variable distances. From the various
appearances which may be observed in the same cartilage, at different
stages of its growth, it would appear that the component cells multiply
by the doubling process already described (§ 248); that they then
separate from one another, each of them drawing towards itself (as it
were) an envelop of intercellular substance ; and that, by the repeti-
tion of the same process, the number of cells in the cartilage may be
indefinitely multiplied. Various stages of this history are shown in the

accompanying figure, which is
f''s-37. taken from a section of the

a J cartilaginous branchial ray of

4^^/^'^^ '"' ""^ ^ ' ^^^ \?irv3. or tadpole of the Rana

'^-"^^^' esculenta, or Edible Frog. In

the centre of the figure are
shown three separate cells,
which have evidently been at
one time in closer proximity
^, with each other. In one of
ti^ these cells, the nucleus is seen
to be developing two new cells
in its interior; and a continua-
tion of this process would give

Section of the Branchial cartilage of Tadpole ; a, risC tO the appearance shown
group of four cells, separating from each other; i, ^^ J where tWO Cclls are shoWn
pairof cells in apposition; c, c, nuclei of cartiluge-cells; «i. i^, y» nv^i v. i v^ v^w ^^ a.^
rf, cavity containing three cells. in cloSC COUtact, being evi-

dently the offspring of the same
parent. Now if each of these cells in like manner develops two
others within itself, a cluster of four will be developed, as shown at
a; and after a time, intercellular substance being accumulated around

I

CARTI..1GE. 169

each, their walls will separate, and they will acquire the character of
distinct cells. It would seem as if, in other cases, one of the first
pair of cells develops another pair in its interior, whilst the other
(from some unknown cause) does not at once proceed to do so; and
thus only three cartilage-cells instead of four are clustered together
in the cavity, as seen at d.

268. The primitive cellular organization now described is retained
in some Cartilages through the whole duration of their existence.
This is the case, for example, in most of the articular cartilages of
joints ; in the cartilaginous portion of the septum narium, in the car-
tilages of the alse and point of the nose, in the semilunar cartilages of
the eyelids ; in the cartilages of the larynx, (with the exception of the
epiglottis,) the cartilages of the trachea and bronchial tubes, the car-
tilages of the ribs, and the ensiform cartilage of the sternum. When
partial ossific deposits take place, it is usually in the substance of
cellular^ rather than in that oi fibrous cartilage.

269. When the intercellular substance, instead of being homo-
geneous, has a fibrous character, the tissue called Fihro- Cartilage is
produced ; and this may be either elastic or non-elastic, according as
the yellow or the white form of fibrous structure prevails. In some
instances, the fibrous structure is so predominant over the cellular,
that the tissue has rather the character of a ligament than of a car-
tilage. The white fibrous structure is seen in all those cartilages,
which unite the bones by synchondrosis, and which are destined not
merely to sustain pressure, but also to resist tension. This is the
case especially in the substances, which intervene between the verte-
brae, and which connect the bones of the pelvis; these in adult Man
are destitute of cartilage-corpuscles, except in and near their centres ;
but in the lower Vertebrata, and in the early condition of the higher,
the fibrous structure is confined to the exterior, and the whole interior
is occupied by the ordinary cartilage-corpuscles. The yellow-fibrous
or reticulated structure is best seen in the epiglottis, and in the concha
of the ear ; in the former of these, scarcely any trace of cartilage-cor-
puscles remains ; and in the latter, the cellular structure is only to be
met w^ith towards the tip.

270. We have seen that the elements of the cellular tissues hitherto
described, do not come into direct contact with the blood-vessels.
The Epidermic and Epithelial cells are separated from them, by the
continuous layer of basement-membrane, which forms the surface of
the true skin, the mucous membranes, the glandular follicles pro-
duced from them, &c. &c. In like manner, the cells of Adipose
tissue are formed within membranous bags ; on the outside of which
the blood-vessels form a minute network. The cells of Cartilage are
not nourished in anymore direct manner; and are sometimes at a
considerable distance from the nearest vessels. It is certain that the
substance of the permanent cellular Cartilages is not permeated, in a
state of health, even by the minutest nutrient vessels ; none such
being brought into view under the highest magnifying power. They

170 CELLS CONNECTED TOGETHER.—CARTILAGE.

are, however, surrounded by vessels, which form large ampxdlce or
varicose dilatations at their edges, or spread over their surfaces ; and
it is by the fluid which is drawn from them by the Cartilage-cells,
that the latter are nourished. The nutrition of a mass of Cartilage
thus seems to bear a strong resemblance to that of the thick fleshy
Sea-weeds, which are in like manner composed entirely of cells, with

Fig. 38.

Vessels situated between the attached synovial membrane, and the articular cartilage, at the point
where the ligamemtum teres is inserted in the head of the os femoris of the human subject, between the
third and fourth months of foetal life ;— a, the surface of the articular cartilage; h, the vessels between
the articular cartilage and the synovial membrane; c, the surface to which the ligamentum teres was
attached ; rf, the vein ; e, the artery.

intercellular substance disposed between them in greater or smaller
amount. The cells in nearest proximity to the nutrient fluid, draw
from it the requisite materials, and transmit these to the cells in the
interior of the mass, receiving a fresh supply in their turn from the
source in their own neighbourhood. When the Articular or other
cellular Cartilages are inflamed, however, we find vessels passing into
their substance; but these vessels are formed in an entirely new tissue,
w^hich is the product of the inflammatory process, and cannot be said
to belong to the Cartilage itself.

271. The temporary Cartilages, which have a like cellular struc-
ture, but which are destined to undergo metamorphosis into Bone,
are equally destitute of vessels when their mass is small ; but if their
thickness exceed an eighth of an inch, they are permeated by canals
for the transmission of vessels. Still these vessels do not ramify with
any minuteness in the tissue ; and they leave large islets^ in which the
nutritive process must take place on the plan just described.

272. The Fibro-Cartilages, formed as it were by the intermingling
of two distinct elementary structures, have a degree of vascularity
proportioned to the amount of the fibrous tissue which they contain ;
but these vessels do not penetrate the cellular portions, where such
are distinct from the mixed structure.

273. The Cartilaginous tissue appears to be more removed than
almost any other in the body, from the general tide of nutritive action.
Its properties are simply of a physical character; and they are not
impaired for a long time after the death of the tissue, its tendency to

CORNEA.— CRYSTALINE LENS.

ni

Fig. 39.

decomposition being very slight, so long as it is exposed to ordinary
temperatures. It is protected by its toughness and elasticity from
those mechanical injuries, to which softer or more brittle tissues are
liable ; and consequently it has little need of any active power of
reparation. It seems doubtful whether, when loss of substance occurs
as a result of disease or accident, this is repaired by real cartilaginous
tissue. In the process of ulceration, as observed by Mr. J. Goodsir,
it appears that the formation of depressions in the surface is due, not
so much to any change originating in the substance of the Cartilage,
as to the eroding action of the cells of the false membrane, which is
the product of inflammatory action upon its surface ; and it is in this
false membrane, that the new vessels are formed, which dip down
into nipple-like prolongations of the membrane, that enter corre-
sponding hollows excavated in the cartilage.

274. The Cornea of the Eye bears a close resemblance to Cartilage,
both in structure and composition ; and it corresponds rather with the
cellular than with the fibrous form of that tissue. The cells are not
so numerous as those of the articular cartilages ; and they are sur-
rounded by a plexus of bright fibres, loosely connected together, so
as to resemble areolar tissue. Two sets of vessels, a superficial and
a deep-seated, surround the margin of
the cornea. The former (Fig. 39, a.)
belong rather to the Conjunctival mem-
brane, which forms the outer layer of the
cornea; and they are prolonged to the
distance of one-eighth or half a line from
its margin, then returning as veins. The
latter (b) do not pass into the true Cornea,
but terminate in dilatations from which
veins arise, just where it becomes con-
tinuous with the sclerotic. In diseased
conditions of the Cornea, however, both
sets of vessels extend themselves through
it. Notwithstanding the absence of ves-
sels in the healthy condition of the
corneal tissue, incised wounds of its
substance commonly heal very readily,
as is well seen after the operation for
Cataract ; but there is a danger in carry-
ing the incision around a large propor-
tion of its margin, lest the tissue should
be too much cut off from the supply of nutriment afforded by the am-
pullae of the vessels that surround it.

275. The Crystaline Lens of the Eye approaches Cartilage, in its
structure and mode of nutrition, more nearly than any other tissue.
It may be separated into numerous laminse ; which are composed of
fibres that lock into one another, by their delicately-toothed margins.
Each of these fibres appears to be made up of a series^of cells, linearly

Nutrient Vessels of the Cornea a.
Superficial vessels Deionging to me
Conjunctival membrane, and continued
over the margin of tlie Cornea ; b. ves-
sels of the Sclerotic, returning at the
margin of the Cornea.

172 CRYSTALINE AND VITREOUS BODIES.— BONE.

arranged, which coalesce at an early period. The lens is not per-
meated by blood-vessels ; at least after it has been completely formed ;
these being confined to the capsule. During the early part of foetal
life, and in inflammatory conditions of the Capsular membrane, both
its anterior and its posterior portions are distinctly vascular; but at a
later period, only the posterior half of the Capsule has vessels distri-
buted upon its surface. It has been shown by optical experiments
devised for the purpose, that a moderate vascularity of the posterior
capsule does not interfere with distinct vision ; whilst if the anterior
capsule were traversed by vessels, the picture on the retina would be
no longer clear. The substance of which the lens is composed ap-
pears to be soluble Albumen, or perhaps more closely resembles the
Globulin of the blood.

276. The Vitreous body, which fills the greater part of the globe of
the eye, also seems to possess a cellular structure ; the cells contain-
ing a fluid, which is little else than water holding in solution a small
quantity of albumen and saline matter ; and the membrane which
forms their walls being so pellucid as to be scarcely distinguishable.
Indeed, the cellular character of this substance is chiefly inferred from
the fact, that when its capsule or enveloping membrane is punctured,
even in several places, the contained fluid does not speedily drain
away, — as it would do if it were merely contained in the interstices
of an areolar tissue. The blood-vessels which traverse the Vitreous
body do not send branches into its substance ; and it must derive its
nutriment from those which are distributed minutely upon its general
envelop, and probably also from the large plexiform vessels of the
ciliary processes of the Choroid coat.

277. We next proceed to examine the nature of the tissues, which
have a cellular structure at their original basis ; but which have
undergone a metamorphosis in regard to the arrangement of their ele-
mentary parts ; and which have received an additional consolidation,
by the deposition of earthy matter in their substance. These tissues
are the Osseous and the Dental, — Bones and Teeth. The structure
of both of them is well adapted to demonstrate the distinction between
the tissues themselves, and those subsidiary parts, by which they are
connected with the rest of the structure. We have seen that Car-
tilage is essentially no7i-vascular ; that is, even when it exists in a
considerable mass, it is not traversed by vessels, but is nourished by
absorption from the fluids contained in the vessels distributed on its
exterior. Now every mass of Bone is penetrated by vessels; never-
theless these do not penetrate its ultimate substance, and may be
easily separated from it, leaving the bone itself as it was. In fact, as
Mr. J. Goodsir observes, " a well macerated bone is one of the most
easily made, and, at the same time one of the most curious anatomical
preparations. It is a perfect example of a texture completely isolated ;
the vessels, nerves, membranes, and fat, are all separated, and nothing
is left but the non-vascular osseous substance." Precisely the same
may be said of the substance of a Tooth, from which the vascular

STRUCTURE OF BONE. 173

lining of the pulp-cavity has been removed ; for it then possesses
neither vessels, nerves, nor lymphatics ; and yet, as we shall presently
see, it has a highly-organized structure, peculiar to itself.

278. The general characters of Osseous texture vary according to
the shape of the Bone, and the part of it examined. Thus in the long
bones, we find the shaft pierced by a central canal, which runs con-
tinuously from one extremity to the other ; and the hollow cylinder
which surrounds this is very compact in its structure. On the other
hand, the dilated ends of the bone are not pene-
trated by the large central canal ; nor are they ^!Ls^
composed of solid osseous substance. They are
made up of cancellated structure, as it is termed ;
that is, of osseous lamellae arid fibres interwoven
together (like those of areolar tissue, on a larger
scale) so as to form a multitude of minute cham-
bers or cancelli, freely communicating with each
other, and with the cavity of the shaft; whilst the
whole is capped with a thin layer of solid bone.
Again, in the thin flat bones, as the scapula, we
find the two surfaces composed of solid osseous
texture, with more or less of cancellated structure Extremity of os fe-
interposed between the layers. And in the thicker ["oris, showing^ancei-
flat bones, as the parietal, frontal, &c., this can- layer ofbone, in contact
cellated structure becomes very distinct, and tTiageJ^6%ancdir ^^^'
forms the diploe ; this, however, is sometimes

deficient, leaving a cavity analogous to the canal of the long bones ;
whilst the plates which form the surfaces of the bone (the external
and internal tables of the skull), resemble in their thickness and soli-
dity, as well as in the intimate structure presently to be described,
the shaft or hollow cylinder of those bones. Finally, we frequently
. meet (especially in the Ethmoid and Sphenoid bones), with thin
lamellae of osseous substance, resembling those which elsewhere form
the boundaries of the cancelli ; these consist of but one layer of bony
matter, and show none of the varieties previously adverted to ; they
are not penetrated by vessels, but are nourished only by their sur-
faces ; and they consequently exhibit to us the elements of the osseous
structure in their simplest form. It will be desirable, therefore, to
commence with the description of these.

279. When a thin natural lamella of this kind is examined, it is
found to be chiefly made up of a substance which is apparently homo-
geneous, but which may be seen (especially after prolonged boiling)
to consist of minute granules, varying in size from l-6000th to
l-14000th of an inch ; these are more or less angular in shape, and
seem to cohere by the medium of some second substance, which is
dissolved by the boiling. They are composed of Calcareous salts,
apparently in chemical union with the Gelatin that forms the basis of
the osseous substance. In the midst of this granular substance a
number of dark spots are to be observed, the form of which is very

174

STRUCTURE OF BONE.

peculiar. In their general outline they are usually somewhat oval;
but they send forth numerous radiating prolongations of extreme
minuteness, which may be frequently traced to a considerable dis-
tance. These spots, known as the osseous corpuscles, (sometimes
termed the Purkinjean corpuscles, after the name of their discoverer,)
are highly characteristic of the true bony structure, being never
deficient in the minutest parts of the bones of the higher animals,
although those of Fishes are frequently destitute of them. These

corpuscles were formerly sup-
^'^- ^^- posed, from their dark appearance,

to be opaque, and to consist of ag-
gregations of calcareous matter
which would not transmit the
light: but it is now quite certain,
that they are lacunce or open
spaces ; and that the radiating pro-
longations from them, which are
far smaller than the minutest capil-
lary vessel, are canaliculi or deli-
cate tubes. Of these canaliculi, some may be seen to interlace freely
with each other, whilst others proceed towards the surface of the
bony lamella ; and thus a system of passages, not by any means wide
enough to admit the blood-corpuscles, but capable of transmitting the
fluid elements of the blood, or matters selected from them, is estab-
lished through the whole substance of the lamella. The lacunae have
an average length of 1- 1800th of an inch ; and they are usually about
half as wide, and one-third as thick. The diameter of the canaliculi

Lacunae of Osseous substance, magnified 500
diameters ;— a, central cavity; b, its ramifications.

is from l-12000th to l-20000th of an inch.

Fis. 42.

Section of the bony scale of Lepidosteus;— a, showing the
regular distribution of the lacunse and of the connecting canali-
culi ; b, small portion more highly magnified.

The succeeding figure
represents the arrange-
ment of these lacunae and
canaliculi in the bony
scale of a Fish (the Lepi-
dosteus) ; which is al-
most the only existing
representative of a large
class of bony-scaled
Fishes, that formerly
tenanted the seas. This
subject is selected on
account of the peculiar
distinctness with which

these elementary parts are shown ; and the entire absence of any of
that more complex arrangement, caused by the penetration of blood-
vessels, which we shall presently have to describe.

280. The lacunae of the solid osseous texture are not unoccupied,
however, in the living Bone. They are filled with a minute granular
substance ; which is probably to be regarded (as first pointed out by
Mr. J. Goodsir) in the light of a germinal spot or nutritive centre,

STRUCTURE OF BONE. 175

that has the power of drawing to itself, through its own system of
canaliculi, the nutritive materials supplied by the blood-vessels on
the nearest surface, and of diffusing these through the surrounding
substance. Between the blood-vessels and the surface of the bony
lamella, however, there is a layer of cells ; which are probably the
immediate agents in the selection and elaboration of the nutritive
matter, and which then deliver it to betaken up by the canaliculi. —
Thus the nutrition of the ultimate osseous texture is carried on upon
the same plan with that of Cartilage ; being effected by the imbibition
of nutrient matter from the surface, through the agency of cells. But
it differs in this ; — that there is a provision in Bone for the ready
transmission of nutrient matter through its texture, by means of minute
channels, which does not exist in Cartilage ; — a difference obviously
required by the greater solidity of the substance of the former, which
does not allow of the diffused imbibition, that is permitted by the
softer and moister nature of the latter. We shall presently find that
they are only formed at a late stage of the development of bone, when
the remaining tissue has acquired its completest consolidation.

281. Now, as already remarked, the simple structure just described
is found, not merely in the delicate plates which form the thinnest
part of certain bones in Man ; but also in those lamellae, which form
the walls of the cancelli of the larger and thicker bones. Every one
of these lamellae repeats, in fact, the same history. The cancelli are
lined by a membrane derived from that of the cavity of the shaft,
over which blood-vessels are minutely distributed ; between these
blood-vessels and the osseous texture, is a layer of cells ; and from
the materials selected and communicated by these, each lamella is
nourished, through its system of radiating canaliculi and nutritive
centres. The cancelli, at the time of their formation in the f<Btal
bone, are entirely filled with such cells ; which appear (as will be
presently explained) to be the descendants of the cells of the original
cartilage ; but in the adult bone, a large proportion of them is filled
with fatty matter, which they secrete into their cavities. — The vessels
of the cancellated structure at the extremities of the long bones, are
derived from those of the medullary cavity, which is penetrated by
large trunks from the exterior ; and in the flat bones, they form a
system of their own, connected with the vessels of the exterior by
several smaller trunks.

282. The solid osseous texture, which forms the cylindrical shafts
of the long bones, and the thick external plates of the denser flat
bones, is not cut off from nutritive action in the degree in which it
might seem to be ; for it is penetrated by a series of large canals,
termed the Haversian, (after Clopton Havers, their discoverer,)
which form a network in its interior, and which serve for the trans-
mission of blood-vessels into its substance. These canals, in the long
bones, run for the most part in a direction parallel to the central
cavity ; and they communicate with this, with the external surface,
with the cancelli, and with each other, by frequent transverse

176

STRUCTURE OF BONE.

Fig. 43.

branches ; so that the whole system forms an irregular network, per-
vading every part of the solid texture, and adapted for the establish-
ment of vascular communications through-
out. The diameter of the Haversian canals
varies from l-2500th to l-200th of an inch,
or more : the smallest being only of sufficient
size#o admit the passage of a single capil-
lary vessel ; whilst the largest receives a
plexus of minute blood-vessels. Their ave-
rage diameter maybe stated at about l-500th
of an inch. They are lined by a membrane,
which is continuous with that of the external
surface, and which carries this inwards (so
to speak) to form the lining membrane of the
central cavity, and of the cancelli. On this
membrane, a plexus of blood-vessels is dis-
tributed, where the size of the canal admits
it; — otherwise, the tube encloses a single
twig of an artery or vein. Thus we may
consider the whole Osseous texture as in-
closed in a membranous bag; on which
blood-vessels are minutely distributed ; and
which is so carried into the bone by invo-
lutions and prolongations, that no part of
the latter is ever far removed from a vascu-
lar surface.

283. Between the vascular lining of the Haversian canals, and
their bony walls, there is a layer of cells ; as in the corresponding
situation in the cancelli : so that it may be stated as a general fact,
that these everywhere intervene between the blood-vessels and the
osseous substance. In the adult bone, the cells which fill the remain-
ing cavity of these canals secrete fatty matter ; this is particularly
evident in the case of the central cavity, where they constitute the
medulla or marrow. It does not appear that these take any active
part in the nutrition of the bone ; indeed in the bones of Birds, the
shaft is entirely hollow, and air is admitted into it from the lungs, so
that its lining membrane is rendered subservient to the aeration of
the blood.

284. The arrangement of the elementary parts of the osseous sub-
stance around the Haversian canals, is very interesting and beautiful.
When a transverse section of a long bone is made, the open orifices
of the longitudinal canals present themselves at intervals, sometimes
connected by a transverse canal, where the section happens to traverse
this. Around these orifices, we see the osseous matter arranged in
the form of cylinders, which appears to be marked by concentric
circles. Now when one of these circles is minutely examined, it is
found to be made up of a series of lacunae, analogous to those already
described ; these, however, are seldom or never so continuous as to

Haversian Canal, seen on a
longitudinal section of the com-
pact lissue of the shaft of one of
the long bones ; 1, arterial canal ;
2, venous canal ; 3, dilatation of
another venous canal.

1

STRUCTURE OF BONE.

177

form a complete circle. The long sides of the lacunse are directed,
the one towards the Haversian canal in the centre, the other towards
the circular row next beyond it. And when the course of the cana-
liculi is traced, it is found that these converge on the inner side
towards the central canal, inosculating with those of the series next
within, whilst those of the outer side pass outwards in a radiating or
diverging direction, to inosculate with those of the series next ex-
ternal. Thus a complete communication is formed, by means of this
system of radiating canaliculi, and intervening lacunse, between the
central canal, and the outermost cylindrical lamella of bony matter ;
and each of these lamellae derives its nourishment from the vessels of
the central canal, through the lamellse which intervene between itself
and the vascular membrane lining that tube.

285. Thus every one of the Haversian canals is the centre of a
cylindrical ossicle; which is complete in itself, as far as its elementary
structure is concerned ; and which has no dependence on, or con-
nection w^ith, other similar ossicles. These are arranged, however,
side by side, like sticks in a faggot ; they are bound together by a
thin cylinder of bone, on the exterior of all, \vhich derives its nourish-
ment from the periosteum or enveloping membrane; in like manner,
the hollow bundle is lined by a similar cylinder, which surrounds the
great medullary cavity, and is nourished by its vascular membrane;
and the spaces that here and there intervene between the ossicles, are
filled up with lamina?, which are parallel to those of the external and
internal cylinders, and which seem to derive their nutriment from
them (Fig. 44, 4). In this manner, the whole structure acquires great

Fig. 44.

Minute structure of bone, dra\ii)n with
tlie microscope from nature. Magnified
800 diameters. 1. One of the Haversian
canals surrounded by its concentric la-
meilee. The corpuscles are seen between
the lamella} ; but the calcigerous tubuli are
omitted. 2. An Haversian canal with its
concentric lamella?, Purkinjean corpuscles
and tubuli. 3. The area of one of the
canals. 4, 4. Direction of the lamellae of
the great medullary canal. Between the
lamellaj at the upper part of the figure,
several very long corpuscles with their
tubuli are seen. In the lower part of the
figure, the outlines of three olher canals are
given, in order to show their form and mode
of arrangement in the entire bone.

density and solidity. — The structure of the outer and inner tables of
the skull, and of other thick solid layers of bone, is precisely similar;
1.*

nS STRUCTURE AND COMPOSITION OF BONE.

except that the Haversian canals have no such definite directions, and
form an irregular network.

286. Thus we see that each of the lamellae of bone, surrounding an
Haversian canal, or bounding the cancelli, may be regarded as a
repetition of the simple bony plate, which draws its nourishment
direct from the vascular membrane covering its surface, by means
of its system of lacunae and canaliculi. The membrane lining the
Haversian canals, cancelli, and central medullary cavity, is an internal
prolongation of that which clothes the exterior; — ^just as the mucous
membranes, with their extensions into glandular structures, are in-
ternal prolongations of the true skin. Every Haversian canal and
every cancellus are repetitions of each other in all essential particulars ;
their form alone being different. The central medullary canal is but
an enlarged Haversian canal or cancellus. And the whole cylin-
drical shaft is a collection of ossicles, each of which is a miniature
representation of itself, being a hollow cylinder, with a central vas-
cular cavity.

287. The principal features of the Chemical constitution of bone
are easily made evident. After all the accessory parts have been
removed, and nothing remains but the real osseous texture, this may
be separated, by simple processes, into its two grand constituents, —
the animal basis, and the calcareous matter. The latter may be
entirely dissolved away, by maceration of the bone in dilute Muriatic
or Nitric acid ; and a substance of cartilaginous appearance is then
left, which, when submitted to the action of boiling water for a short
time, is almost entirely dissolved away, and the solution forms a dense
jelly on cooling. The same substance, Gelatin, may be obtained by
long boiling under pressure, from previously unaltered bone ; and the
calcareous matter is then left in a friable condition. By submitting a
bone to a heat sufficient to decompose the animal matter, without
dissipating any of the earthy particles, we may obtain the whole
calcareous matter in situ; but the slightest violence is sufficient to
disintegrate it. The bones of persons long buried are often found in
this condition; their form and position being retained, until they are
exposed to the air, or are a little shaken ; when they crumble to dust.
— The proportion of the earthy matter of Bones to the animal basis
may be differently stated ; according as we include in our estimate of
the latter, the contents of the medullary cavity, the Haversian canals,
and the cancelli ; or confine ourselves to that portion only of the ani-
.mal matter, which is united with the calcareous element in the proper
-osseous tissue. According to the recent experiments of Dr. Stark,*
the relative amount of the two elements, in the latter estimate, is
subject to very little variation, either in the different classes of ani-
mals, or in the same species at different ages; the animal matter
composing about one-third, or 33J per cent. ; and the mineral matter
two-thirds, or 66| per cent. The degree of hardness of bone does

♦ Edinburgh Medical and Surgical Journal, April, 1845.

COMPOSITION OP BONE. 179

not altogether depend, therefore, on the amount of earthy matter they
may contain ; for the flexible, semi-transparent, easily-divided bones
of Fish contain as large an amount of animal matter, as the ivory-like
leg-bones of the deer or sheep. The usual analyses of Bone, how-
ever, have been made upon the former kind of estimate; and they
show that the proportion of the earthy matter to the whole of the
animal substance contained in bone, varies much in different animals,
in the same animal at different ages, and even in different parts of the
same skeleton. The reason of this will be apparent, when the history
of the growth of Bone has been explained ; since there is a gradual
filling-up of all the cavities at first occupied by fat-cells, vessels, &c.,
which does not cease with adult age, but which continues during the
whole of life. In this manner, the bones of old persons acquire a
high degree of solidity, but they become brittle in proportion to their
hardness. From the same cause, the more solid bones contain a
larger proportion of bone-earth than those of a spongy or cancellated
texture ; the temporal bone, for example, containing 63J^ per cent.,
whilst the scapula possesses only 54 per cent. In the former of
these bones, the proportion is nearly the same as that which exists
in pure osseous tissue, the amount of the remaining tissues which it
includes being very small, on account of the solidity of the bone: but
the latter contains in its cancelli a large quantity of blood-vessels,
fat-cells, &c., which swell the proportion of the animal matter from
33^ to 46 per cent.

288. The Lime of bones is, for the most part, in a state of Phos-
phate, especially among the higher animals ; the remainder is a Car-
bonate. In Human bones, the proportion of the latter seems to be
about one-sixth or one-seventh of the whole amount of bone-earth.
In the bones of the lower animals, however, the proportion of Car-
bonate is greater ; and it is curious that in callus, exostosis, and other
irregular osseous formations in the higher animals, the proportion of
the Carbonate should be much greater than in the sound bone. In
caries, however, the proportion of the Carbonate is less than usual.
The composition of the Phosphate of Lime in Bones, is somewhat
peculiar; eight proportions of the base being united with three of the
acid. According to Professor Graham, it is to be regarded as a com-
pound of two tribasic phosphates ; one atom of the neutral phosphate
(in which one proportional of the acid is united with two of lime and
one of water), being united with two proportionals of the alkaline
phosphate, (in which one part of acid is united with three of the base,)
together with an atom of water, which is driven off by calcination.
Besides these components, some Chemists assert that a small quantity
of Fluoride of calcium is present in Bone ; but this is rather doubtful,
since it has been shown by Dr. G. O. Rees that the solvent action
upon glass, which has been supposed to be characteristic of fluoric
acid, may be imitated by phosphoric acid in combination with water,
which, if heated upon glass of inferior quality until it volatilizes, will
act upon it with considerable energy. — Other saline matters, such as

180 SKELETONS OF INVERTEBRATA.

phosphate of magnesia, oxides of iron and manganese, and chloride
of sodium, are found in bones in small amount.

289. The purpose of Bone in the Animal economy is obviously
mechanical^ and that only ; its use being, to afford support and pro-
tection to the softer textures, and to form inflexible levers, by the
action of the muscles upon which, motion 'may be given to the dif-
ferent parts of the fabric. A slight comparison of the characters and
offices of the Bones of Vertebrated Animals, with the structures which
form the solid skeletons of the lower classes, will afford many points
of interest ; and will aid in the comprehension of the purpose of the
highly-elaborate structure we have been considering. Commencing
with the Polypifera, or Coral-forming animals, we observe that their
strong axes or sheaths are destined only to give support to their softer
structures, and that the parts once consolidated undergo no subse-
quent change. It was formerly imagined, that the stony Corals were
built up by the animals which form them, somewhat in the same
manner as a Bee constructs its cell. But it is now fully demonstrated,
that the calcareous matter (which here consists solely of the Carbonate
of Lime) is deposited in the cells of the living tissue, by a secreting
action of their own ; and that the most solid mass of Coral thus has
an organized basis, as complete as that of Bone. The proportion of
earthy to animal matter, however, is so great in the former structures,
that very little, if any, nutrient changes can take place in their tissue,
when once it has become consolidated. Such changes are not, how-
ever, required. The substance thus developed by the wonderful
secreting powers of the lime-secreting cells, which draw into them-
selves the small quantity of calcareous matter dissolved in the sur-
rounding water, is so little disposed to undergo change, that it will
maintain its solidity for centuries ; and even when acted on by water
or by heat, it does not undergo disintegration, for its calcareous par-
ticles arrange themselves in a new method, and become converted
into a solid crystaline rock. Such rocks, the product of the meta-
morphosis of ancient coral-formations, make up a large proportion of
the external crust of the earth. The solid stem or sheath, once
consolidated, appears to undergo no further change in the living
Coral-structure ; for its increase takes place, not by interstitial but
by superficial deposit, — that is, not by the diffusion of new matter
through its whole substance, separating the parts formerly deposited
from each other, but by the mere addition of particles to its surface
and extremities. In this manner the growth of a solid Coral-structure
may go on to an enormous extent ; the surface at which the consoli-
dating action is going on, being the only part alive, that is exhibiting
any vital change ; and all the rest of the mass being henceforth per-
fectly inert.

290. In the class of Echinodermata, which includes the Star-fish,
Sea-Urchin, &c., we find the calcareous structure presenting a very
elaborate organization ; as an example of this, we shall select the shell
of the Echinus, commonly known as the Sea-Egg. This shell is made

SHELL OF ECHINODERMATA.

181

up of a number of plates, more or less regularly hexagonal, and fitted
together so as completely to enclose the animal, except at two points,
one of which is left open for the mouth, the other for the anus. On
the surface of these plates are little tubercles, for the articulation of
the spines, which serve as instruments of defence and of locomotion.
The substance of the shell and of the spines is exactly alike ; being a
sort of areolar tissue, consolidated by the deposition of calcareous
matter, and having an innumerable series of interspaces or minute
cancelli, freely communicating with each other. The arrangement of
this calcareous network in the spines, is most varied and elaborate ;
and causes thin sections of them to be among the most beautiful of
all microscopic objects. The external and internal surface of each
plate, in the shell of the living Echinus, is covered with a membrane,

Fig. 45.

oooooooooooapy
Ooooo "^"^

Portion of the shell of the Echinus, showing at a the constituent plates with the calcified areolar
tissue, of which they are composed, at b.

from which its nutrition is derived ; this membrane dips down into
the spaces between the adjacent plates ; but it does not penetrate the
substance of the plates themselves, nor does it transmit vessels to their
interior. A similar membrane covers and encircles the spines; and
it also connects these with the shell, being continuous with the mem-
brane that envelops the latter. Thus each plate and spine is itself
completely extra-vascular; but it is enclosed in a soft membrane, which
furnishes (whether by vessels or otherwise, has not yet been ascer-
tained), the elements of its nutrition.

* 291. But we do not here find any evidence of interstitial growth ;
nor is there any reason why such should be required. For the tissue
of which it is composed, although of such extreme delicacy, is of
great permanence, and does not exhibit the slightest tendency to
decay, however long it is preserved ; so that, when once consolidated,
it appears to undergo no further change in the living animal. The
growth of the animal, however, requires a corresponding enlargement
of its enveloping shell ; and this is provided for by the simple process
of superficial deposit, through the subdivision of the whole shell into
component plates. For by the addition of new matter at the edge of

182 SHELLS OF MOLLUSCA.

eachplate^ by the consolidation of a portion of the soft membrane that
intervenes between the adjacent plates, the whole shell is enlarged,
■without losing its globular form. At the same time it is strengthened
in a corresponding degree, by the consolidation of the soft tissue at
the surface of each plate. And, in like manner, the spines are en-
larged and lengthened by the progressive formation of new layers,
each on the exterior of the preceding ; so that a transverse section
exhibits a number of concentric rings, like those of an Exogenous
tree. — Thus even in the growth of this complex and elaborate struc-
ture, we recognize the principle of superficial deposit, which we shall
find to be universal amongst the hard parts of the Invertebrata ; not-
withstanding that, at first sight, it would have appeared impossible to
provide on this plan for the gradual enlargement of a globular shell,
completely enclosing the animal, and therefore required to keep pace
with the latter in its rate of increase.

292. Among the Mollusca, we find the body sometimes altogether
destitute of solid organs of support, protection, or locomotion, — as is
the case, for example, in the Slug; and the movements are feeble and
the habits inert, the muscle having no fixed points for their attach-
ment, and acting without any of the advantages of leverage. In other
cases, we find the body more or less completely protected by a Shell ;
which is suflficiently large in some instances to cover the body com-
pletely ; whilst in others, it affords only a partial investment. The
plan on which this shell is formed, however, is very different from
that which has just been described ; being much less complex. The
Univalve shells, or those formed in one piece, are always of a conical
form ; the cone being sometimes simple, as in the Limpit ; in other
cases being spirally coiled, as in the Snail. Now the base of this
cone is open ; and through this, the animal can project its movable
parts. When its increasing size requires additional accommodation,
it is obvious that an addition to the large end of the cone will increase
its diameter and its length at the same time ; so as to afford the re-
quired space, without any alteration in the form or dimensions of the
older and smaller portions of the cone. This last, indeed, is fre-
quently quitted by the animal, and remains empty ; being sometimes
separated from the latter portions, by one or more partitions thrown
across by the animal, — as is seen especially in the Nautilus and other
chambered shells. Besides the new matter added to the mouth of
the shell, a thin layer is usually formed over its whole interior sur-*
face; so that the lining of the new part is continuous with that of the
old. — In the Bivalve shells, we trace this mode of increase without
any difficulty; especially in such shells as that of the Oyster, in which
the successive laminae remain distinct. Each lamina is interior to the
preceding, being formed on the living surface of the animal ; but it
also projects beyond it, so as to enlarge the capacity of the shell ; and
as the separation of the valves affords free exit to those parts of the
animal, which are capable of being projected beyond the shell, there
is obviously no need of any other provision to maintain the shell in

SHELLS OF MOLLUSCA.

183

its natural form. — Thus in the shells of the Mollusca, increase takes
place at the surfaces and edges only.

293. The proportion of organic and calcareous matter in Shell
differs considerably in the various tribes. The former is sometimes
present in such small amount, that it can scarcely be detected; and
the condition of the calcareous matter then obviously approaches that
of a crystaline deposit. But in other instances, the animal basis is
very obvious; remaining as a thick consistent membrane, after all the
calcareous matter has been dissolved away by an acid. This mem-
brane is formed of an aggregation of cells arranged with great regu-
larity (Fig. 46, a;) the cavities of which are filled with carbonate of

Fig. 46. <*

Prismatic cellular structure of shell of Pinna; a, surface of lamina; fc, vertical section.

lime in a crystaline state. The form of the cells approaches the
hexagonal; their diameter varies in different shells from 1-lOOth to
l-2800th of an inch ; their thickness also is extremely variable, even
in different parts of the same shell. Thus we sometimes meet with a
lamina of such tenuity, as not to measure 1-lOOth of an inch in thick-
ness; whilst in other instances, a single layer may have a thickness
of half an inch, or even (in certain large fossil species) of an inch or
more. In this case, the cells, instead of being thin flat scales like the
pavement-epithelium (§ 233), are long prisms, somewhat like the
cells of the cylinder-epithelium (Fig. 22), with their walls flattened
against each other. The appearance which is then presented by a
vertical section of them, is represented in Fig. 46, 6. The long
prismatic cells are there seen to be marked by delicate transverse
striae ; and these, taken in connection with other indications, appear
to show, that every such prism is in reality formed by the coalescence
of a pile of flat cells, resembling those which are seen in the very thin
laminae just described ; so that the thickness of the layer depends upon
the number of the cellular lamina?, which have coalesced to form its
component prisms. This character is of interest, as representing on
a magnified scale a corresponding appearance in the enamel of human

184 SKELETON OF ARTICULATA.

Tooth, which we shall presently find to be formed upon the very same
plan.

294. We are to regard this kind of shell-substance, therefore, as
formed by the secreting action of the epithelial-cells covering the
mantle of the animal, — which membrane, though it answers in posi-
tion to the skin, has the soft, spongy, glandular character of a mucous
membrane. These draw calcareous matter into their cavities, as a
part of their own process of growth ; this matter being supplied from
the fluids of the vascular surface beneath. Now when these cal-
cigerous cells are separated by intercellular substance, they remain
distinct through the whole of their lives, and they form by their cohesion
a tenacious membrane, that retains its consistency after the removal
of the calcareous Aatter. But this is only the case in certain groups
of shells, chiefly belonging to the bivalve division. When the inter-
cellular substance is wanting, and the cells come into close contact,
their partitions become indistinct on account of their extreme tenuity;
and not unfrequently a fusion of the whole substance appears to take
place, by the dissolution of the original cell- walls, so that it becomes
more or less homogeneous, — traces of the original cellular structure
being here and there distinguishable (§ 255).

295. Sometimes where this fusion has taken place, so as to oblite-
rate the original cell-structure, we find the almost homogeneous sub-
stance traversed by a series of tubuli, not arranged, however, in any
very definite direction, but forming an irregular network. These

tubes vary in size from l-2000th
^'^^''' to l-20,000th of an inch; but

their general diameter, in the
shells in which they most abound,
is l-4500th of an inch. In the
larger tubuli, something of a
bead-like structure may occa-
sionally be seen ; as if their in-
terior were occupied by rounded
granules arranged in a linear
direction. Although it might be
supposed that this structure is
destined to convey nutrient fluid into the substance of the shell, yet
there is no evidence that such is the fact ; and, on the contrary, there
is ample evidence, that, even in shells most copiously traversed by
these tubuli, no processes of interstitial growth or renewal take place.
The permanent character of the substance of all Shells, when once it
is fully formed, is as remarkable as that of Coral; and as the adapta-
tion of their size, to that of the animals to which they belong, is en-
tirely eflfected by additions to their surfaces and edges, no interstitial
deposit can have a share in producing it.

296. Among the Articulated classes, we still find that the skeleton
as altogether external, and belongs therefore to the cutaneous system ;
but it is formed upon a very different plan from the shells of the Mol-

Tubular shell-structure, from Anomia.

MOULTING.— SHELLS OF CRUSTACEA. 185

lusca, being closely fitted to the body, and enveloping every part of
it ; consequently it must increase in capacity, with the advancing
growth of the contained structures. Moreover it is destined not
merely to afford support and protection to these, but to serve for the
attachment of the muscles by which the body and limbs are moved ;
and the hard envelops of the latter serve, like the bones of the Verte-
brata, as levers by which the motor powers of the muscles are more
advantageously employed. Again, the hard envelops of the body and
limbs are not formed of distinct plates, like those of the Echinus-shell,
but are only divided by sutures at the joints, for the purpose of per-
mitting the requisite freedom of motion. It might have been thought
that here, if anywhere, a process of interstitial growth would have
existed, to adapt the capacity of the envelops to the dimensions of
the contained parts, as the latter increase with the growth of the
animal ; but, true to the general principle, that epidermic structures
are not only extra-vascular, but that they undergo no change when
they are once fully formed, we find that the hard envelops of Articu-
lated animals are thrown off, or exuviated, when the contained parts
require an increase of room ; and that a new covering is formed from
their surface, adapted to their enlarged dimensions.

297. This is well known to occur at certain intervals in Crabs,
Lobsters, and other Crustacea ; which thus exuviate not merely the
outer shell, with the continuation of the epidermis over the eyes, but
also its internal reflexion, which forms the lining of the oesophagus
and stomach, and the tendinous plates by which the muscles are
attached to the lining of the shell. A similar moulting may be ob-
served to occur in some of the minute Entomostracous Crustacea of
our pools, every two or three days, even after the animals seem to be
full grown. During the early growth of Insects, Spiders, Centipedes,
&c., a similar moult is frequently repeated at short intervals ; but after
these animals have attained their full growth, which is the case with
Insects at their last change, no further moulting takes place, the
necessity for it having ceased. — This moulting is precisely analogous
to the exfoliation and new formation of the Epidermis, in Man and
most other Vertebrata; differing from it only in this, that the latter is
constantly taking place to a small extent, whilst the former is com-
pletely effected at certain intervals, and then ceases. We have ex-
amples of a periodical complete moult in Vertebrata, however, among
Serpents and Frogs.

298. The structure of the hard envelops of Articulated animals
corresponds with that of the Epidermis and its appendages in Man.
The firm casings of Beetles, for example, are formed of layers of
epidermic cells, united together, and having their cavities filled by a
horny secretion. The densest structure is found in the calcareous
shells of the Crustacea ; which consist of a substance precisely analo-
gous to the Dentine of Teeth (§ 311); covered on the exterior with a
layer of pigment-cells. The calcareous matter consist chiefly of car-
bonate of lime; but traces of the phosphate are also found. The

186 BONE OF VERTEBRATA.

animal basis has a firm consistent structure, resembling that of teeth.
A thin vertical section shows the tubuli running nearly parallel, but
with occasional undulations, from the internal surface towards the
external ; but no traces of the original calcigerous cells can be detected
in the fully-formed shell, the process of fusion having gone so far as
to obliterate them. The manner in which these tubuli are formed,
will be presently considered, under the head of Dental substance.

299. Now the condition of the osseous skeleton of Vertebrated
animals is altogether ditFerent. It forms a part of the internal sub-
stance of their bodies ; and as these grow in every part, and not
merely by addition to this or that portion, so must the Bones also,
in order to keep pace with the rest of the structure. Hence we
find them so formed, that the processes of interstitial deposition may
be continually going on in their fabric, as in that of the softer tissues ;
and the changes in their substance do not cease, even when they have
acquired their full size. The continuance of these changes appears
destined, not so much to repair any waste occasioned by decomposi-
tion,— for this must be very trifling in a tissue of such solidity, — as to
keep the fabric in a condition, in which it may repair the injuries in
its substance occasioned by accident or disease. The degree of this
reparative power is proportional, as we shall presently see, to the
activity of the normal changes, which are continually taking place in
the bone ; and is thus much greater in youth than in middle life, and
greater in the vigour of manhood than in old age.

300. We shall commence the history of the development of Bone,
with the period in which its condition resembles that of the permanent
Cartilages. As already mentioned, there is no essential difference
between the temporary and permanent Cartilages, in regard to their
ultimate structure ; the former, however, are more commonly traversed
by vessels, especially when their mass is considerable. These ves-
sels, however, do not pass at once from the exterior of the cartilage
into its substance ; but they are conveyed inwards along canals, which
are lined by an extension of the perichondrium or investing mem-
brane, and which may thus be regarded as so many involutions of
the outer surface of the cartilage. These canals are especially de-
veloped at certain points, which are to be the centres of the ossifying
process ; of these puncta ossificationis, we usually find one in the
centre of the shaft of a long bone, and one in each of its epiphyses ;
in the flat bones there is one in the middle of the surface, and one in
each of the principal processes. Up to a late stage of the ossifying
process, the parts which contain distinct centres are not connected by
bony union, so that they fall apart by maceration ; and even when
they should normally unite, they sometimes remain separate, — as in
the case of the Frontal bone, in which we frequently meet with a
continuation of the sagittal suture down the middle, dividing it into
two equal halves, which have originated in two distinct centres of
ossification. It is interesting to remark that, in the two lowest classes
of Vertebrata, — Fishes and Reptiles, — we find the several parts of

CONVERSION OF CARTILAGE INTO BONE.

187

the osseous system presenting, in a permanent form, many of the
conditions which are transitory in the higher ; thus the different por-
tions of each vertebra, the body, lateral arches, spinous and transverse
processes, &c., which have their distinct centres of ossification, but
which early unite in Man, remain permanently distinct in the lower
Fishes ; the division of the frontal bone, just adverted to, is constant
amongst Reptiles ; and in that class we meet with a permanent sepa-
ration of the parts of the occipital and temporal bones, which, being
formed from distinct centres of ossification, are at first distinct in the
higher animals.

301. During the formation of the pundum ossificationis, and the
spread of the vessels into the cartilaginous matrix, certain changes
are taking place in the substance of the latter, preparatory to its con-
version into bone. Instead of single isolated cells, or groups of two,
three, or four, such as w^e have seen to be characteristic of ordinary
Cartilage, (§ 267,) we find, as we approach the ossifying centre,
clusters made up of a larger number, which appear to be formed by a
continuance of the same

multiplying process as ^'^s- 4S.

that already described.
And when we pass still
nearer we see that these
clusters are composed
of a yet greater number
of cells, which are ar-
ranged in long rows,
w^hose direction corre-
sponds with the longitu-
dinal axis of the bone ;
these clusters are still
separated by intercellu-
lar substance, and it is
in this, that the ossific matter is first deposited

Section of Cartilage, near the seat of ossification; each single
cell having given birth to four, five or six cells, which form clus-
ters. These clusters become larger toveards the right of the
figure, and their cells more numerous and larger; their long di-
ameter being l-1500th of an inch.

Thus if we separate

Fig. 49.

m^M
(d

The same cartilage at the seat of ossification ; the clusters of cells are arranged in columns ; the in-
tercellular spaces between the columns being l-3250th of an inch in breadth. To the right of the figure,
osseous fibres are seen occupying the intercellular spaces at first bounding the clusters laterally, then
splitting them longitudinally and encircling each separate cell. The greater opacity of the right hand
border is due to a threefold cause, the increase of osseous fibres, the opacity of the contents of the
cells, and the multiplication of oil-globules.

188 PRODUCTION AND GROWTH OF BONE.

the cartilaginous and the osseous substance at this period, we find
that the ends of the rows of cartilage-cells are received into deep
narrow cups of bone, formed by the transformation of the intercellu-
lar substance between them. Immediately upon the ossifying surface,
the nuclei, which were before closely compressed, separate considera-
bly from one another, by the increase of material within the cells ; and
the nuclei themselves become larger and more transparent. These
changes constitute the first stage of the process of ossification, which
extends only to the calcification of the intercellular substance ; in
this stage there are no blood-vessels directly concerned. The bony
lamellae thus formed, mark out the boundaries of the cancelli and
Haversian canals ; which are afterwards to occupy a part of the space
that is hitherto filled by the rows of cartilage-corpuscles.

302. The second stage of the ossifying process consists in the fur-
ther transformation of the original cartilage-cells. These seem to be-
come flattened against the osseous layers already formed, and then to
become themselves consolidated by the secretion of calcareous mat-
ter into their interior, — at the same time coalescing to such a degree,
that the original boundaries of the cells can no longer be traced.
The consolidation, however, does not extend to the nuclei of the
cells ; which retain their granular condition, and, being surrounded
by calcareous matter, are enclosed in cavities which take their own
shape. These cavities are the subsequent lacunce of the bony struc-
ture ; and the branching canaliculi proceeding from them become
more and more distinct, as the consolidation of the surrounding struc-
ture is completed. By the continuation of this process, one layer of
cells after another is converted into bony matter ; and the canals,
which at first occupied the whole diameter of the cylindrical ossicles
shown in Fig. 44, become gradually contracted by these deposits upon
their walls. The cause of the concentric lamination of the osseous
matter in each of the ossicles, of which the permanent Haversian
canal is the centre, is thus apparent.

303. As the calcification of the original cartilage-cell goes on, a
new substance appears in the cavities of the cancelli and canals ;
this is a cellular mass resembling that in which all new tissues origi-
nate ; and it seems to be from this, that the vascular lining is formed,
which gradually extends itself into the cancelli and canals, and which
is to become from henceforth the principal source of the growth and
nutrition of Bone. From the central part of this blastema, the fat-
c6lls, constituting the medulla, must be generated. But, as already
stated (§ 283), a layer of cells resembling the originals constantly
intervenes between the bony walls of the canals and cancelli, and
their vascular lining ; apparently for the purpose of serving as the
immediate agent in the nutrition of the osseous tissue.

304. When the complete Ossification of the temporary Cartilage
has thus been effected, the Bone has still to be enlarged, in conformity
w^ith the increasing size of the surrounding parts ; and this enlarge-
ment is due in part to superficial^ in part to interstitial addition. The

GROWTH OF BONE. 189

superficial addition is due to the progressive formation and conversion
of new cartilage at the edges and surfaces of the bone, or at the im-
perfectly-consolidated part that intervenes between the separately-
ossified portions of the same bone. Thus it was long since proved by
the experiments of Hales and Hunter, that the growth of a long bone
takes place chiefly towards the extremities ; for they found that, when
metallic substances were inserted in the shaft of a growing bone of a
young animal, the distance between them was but little altered after
a long interval, whilst space between the extremities of the bone had
greatly increased. And it seems that, at a later period, when the
epiphyses have become completely united to the shaft, an elongation
continues to take place, by the slow ossification of the articular carti-
lage.— Again, the bone is progressively increased in thickness, by
the gradual production of new osseous matter upon its surface ; this
production taking place exactly upon the same plan with the original
process, and involving the formation of new Haversian canals and
concentric lamellae, so that no distinction can be traced between the
new and the older layers.

305. If this were the whole history of the growth of Bone, there
would be no essential difference between the character of its nutri-
tion, and that of the skeletons of the Invertebrata. But it is unques-
tionable, that bone is also susceptible of an interstitial change, though
this is of a slow and gradual nature. The layers first deposited on
the inner surface of the early cancelli, are pushed outwards by the
succeeding ones, and gradually acquire an increased diameter ; so
that the ultimate dimensions of the cancelli and cylindrical ossicles
far exceed those of the primitive cavities marked out by the calcifi-
cation of the intercellular substance ; and this last, also, must be
greatly extended to permit such an increase. This process could not
go on beyond a certain point, however, without removing the outer
laminae too far from the vascular lining of the Haversian canals ; and
we consequently find that the increase of the bone takes place by
superficial addition, wherever this is admissible. — A very remarkable
change takes place in the interior of the long bones of young animals,
for the production of the central medullary cavity. At an early pe-
riod, no such cavity exists, and its place is occupied by small can-
celli ; this is the permanent condition of the bones in most Reptiles.
The cancelli gradually enlarge, however; and those within the shaft
coalesce with one another until a continuous tube is formed, around
which the cancelli are large, open, and irregular. At the same time,
the diameter of the surrounding shaft is increasing by the process of
interstitial growth just described ; so that the size of the medullary
cavity at last becomes greater than that of the whole shaft when its
formation commenced. The aggregation of the osseous matter in a
hollow cylinder, instead of a solid one, is the form most favourable
to strength, as may be easily proved upon mechanical principles. The
same arrangement is adopted in the arts, wherever it is desired to
obtain the greatest strength with a limited amount of material.

190 GROWTH AND REGENERATION OF BONE.

306. The difference in the relations of the Osseous substance to
the vascular network, at different ages, — accounting for the varia-
tions in the rapidity of its nutrition and reparation, — is well displayed
in the effects of Madder. This substance has a peculiar affinity for
Phosphate of Lime ; so that when the latter is formed by precipita-
tion in a fluid tinged with madder, it attracts colour to it in its de-
scent, and falls to the bottom richly tinted. Now when animals are
fed with this substance, it is found that their bones become tinged
with it ; the period required being in the inverse proportion to their
age. Thus in a very young animal a single day suffices to colour
the entire skeleton, for in them there is no osseous matter far from
the vascular surfaces ; when sections are made, however, of the bones
thus tinged, it is found that the colour is confined to the immediate
neighbourhood of the Haversian canals, each of which is encircled
by a crimson ring. In full-grown animals, the bones are very slowly
tinged ; because the osseous texture is much more consolidated and
less permeable to fluid than in earlier life ; and because, owing to
the formation of new concentric lamellae, the outer and older ones
are pushed to a greater distance from the Haversian canals, the di-
ameter of which is contracted. In the bones of half-grown animals,
a part of the bone is nearly in the perfect condition, while a part is
new and easily coloured ; so that the action of this substance enables
us to distinguish the new from the old.

307. The Regeneration of Bone, after loss of its substance by dis-
ease or injury is extremely complete ; in fact there is no other struc-
ture of so complex a nature, which is capable of being so thoroughly
repaired. Although the regenerative power appears to be so much
less in Vertebrated animals^ than it is in the lower Invertebrata, yet
it is probably not at all lower in reality, — the new structures actually
formed being as complex in the one case as in the other. It is no-
where, perhaps, more remarkably manifested, than in the reformation
of nearly an entire bone, when the original one has been lost by dis-
ease ; all the attachments of muscles and ligaments, as well as the
external form and internal structure, being ultimately found as com-
plete in the new bone, as they originally w^ere in that which it has
replaced. Much discussion has taken place in regard to the degree,
in which the different membranous structures, that surround bone and
penetrate its substance, participate in its regeneration ; some having
supposed the periosteum to have the power of itself ybrmi??^ new
bone, others attributing the same power to the membrane lining the
medullary cavities. It appears next to certain, however, that new
osseous tissue can only be formed in continuity with that which pre-
viously existed ; and that it may be generated, by the mediation of
even very minute fragments of such tissue, from any of the vascular
membranes that happen to supply it. Thus when the portion of the
shaft of a bone is entirely removed, but the periosteum is left, the
space is filled up with new bony matter in the course of a few weeks;
though, if the periosteum be also removed, the formation of new mat-

REPARATION OF BONE. 191

ter will be confined to a small addition in a conical form to the two
extremities, a large interspace intervening between them. This expe-
riment might seem to indicate, that the periosteum itself forms the
bone ; but the real production of new tissue, — as in cases where the
periosteum has been detached by disease, and remains alive whilst
the shaft dies, — is in continuity with minute spicula of the original
bone, which still adhere to the periosteum.* Again, we find that in
comminuted fractures, every portion of the shattered bone that remains
connected with the vascular membranes, whether these be the internal
or the external, becomes the centre of a new formation ; and that the
loss of substance is filled up the more rapidly, in proportion to the
number of such centres.

308. The reparation of Bone, after disease or injury, takes place
exactly upon the same plan as its first formation. A plastic or organ-
izable exudation is first poured out from the neighbouring blood-ves-
sels, and this forms a sort of bed or matrix, in which the subsequent
processes take place. Next, a cartilaginous substance is formed, as
in the embryo, by the attraction of gelatinous intercellular substance
to the exterior of certain cells, and this is gradually converted into
Bone, by the regular process of ossification. When the shaft of a
long bone has been fractured through, and the extremities have been
brought evenly together, it is found that the new matter first ossified
is that which occupies the central portion of the deposit, and which
thus connects the medullary cavities of the broken ends, forming a
kind of plug that enters each. This was termed by Dupuytren, by
whom it was first distinctly described, Xhe provisional callus. This is
usually formed in the course of five or six weeks, or less in young
persons ; but at that period the contiguous surfaces of the bone itself
are not cemented by bony union ; and the formation of the permanent
callus occupies some months, during which the provisional callus is
gradually absorbed, and the continuity of the medullary canal restored,
in the same manner as it was at first established. The permanent
callus has all the characters of true bone.

309. The most extensive reparation is seen, when the shaft of a
long bone is destroyed by disease. If violent inflammation occur in
its tissue, the death of the fabric is frequently the consequence, — appa-
rently through the blocking-up of the canals with the products of the
inflammatory action, and the consequent cessation of the supply of
nutriment. It is not often that the whole thickness of the bone
becomes necrosed at once ; more commonly this result is confined to
its outer or its inner layers. When this is the case, the new formation
takes place from the part that remains sound ; the external layers,
which receive their vascular supply from the periosteum and from the
Haversian canals continued inwards from it, throwing out new matter
on their interior, which is gradually converted into bone; whilst the
internal layers, if they should be the parts remaining uninjured, do

* See Mr. J. Goodsir on the Reproduction of Bone, in his Anatomical and Patho-
logical Researches.

192

FORMATION OF TEETH.—DENTINE.

the same on their exterior, deriving their materials from the medul-
lary membrane and its prolongations into their Haversian canals. But
it sometimes happens that the whole shaft suffers necrosis ; and as
the medullary membrane and the entire system of Haversian canals
have lost their vitality, reparation can only take place from the splin-
ters of bone which remain attached to the periosteum, and from the
living bone at the two extremities. This is consequently a very slow
process ; more especially as the epiphyses, having been originally
formed as distinct parts from the shaft, do not seem able to contribute
much to the regeneration of the latter.*

310. We next proceed to the Teeth^ which are organs of mechanical
attrition, developed in the first part of the alimentary canal, for the

purpose of comminuting the food con-
^'^■^^- veyed into it. Their place of origin is

altogether different from that of bone, as
they commence in little papillary eleva-
tions of the mucous membrane covering
the jaw; but the substance from which
they are formed is the same primitive
cellular tissue, as that in which Cartilage
itself originates. We may best under-
stand the structure and development of
the Teeth in Man, by first inquiring into
the characters presented by those of some
of the lower animals, and the history of
their evolution. In the foetal Shark, the
first appearance of the tooth is in the form
of a minute papilla on the mucous mem-
brane covering the jaws; the substance of
this papilla is composed of spherical cells,
which are imbedded in a kind of gela-
tinous substance resembling that of inci-
pient cartilage ; whilst its exterior is com-
posed of a dense, structureless, pellucid
membrane. The cellular mass is not at
first permeated by vessels; but a small
arterial branch is distributed to each papilla, and spreads out into a
tuft of capillaries at its base (Fig. 50). The papilla gradually enlarges,
by the formation of new cells at the part immediately adjacent to the
blood-vessels, which supply the material requisite for their develop-
ment; and when it has acquired its full size, the process o^ calcifica-
tion takes place, by which it is converted into Dentine, — the substance
most characteristic of teeth.

311. This Dentine, which in the Elephant's tusk is known as Ivory,

* For many parts of the foregoing account of the structure and development of
Bone, the Author is indebted to the Chapter on that subject in Messrs. Todd and
Bowman's Physiological Anatomy, as well as to the papers of Mr. Goodsir already
referred to.

Vessels of Dental Papilla.

STRUCTURE OF DENTINE.

193

Fig. 51.

Oblique section of Dentine of hu^-
man tooth, highly magnified, show-
ing the calcigerous tubuli, and lh«
outlines of the original cells.

is a firm substance, in which mineral matter predominates to a greater
extent than in bone; but which still has a definite animal basis, that
retains its form when the calcareous matter has been removed by
maceration in acid. In every 100 parts, the animal matter fi^rms
about 28 ; and of the mineral portion phosphate of lime constitutes
about 64J parts, carbonate of lime 5J parts, and phosphates of mag-
nesia and soda, with chloride of sodium, about 2J parts. When it
is fractured, it seems to possess a fibrous
appearance ; the fibres radiating from the
centre of the tooth towards its circumfe-
rence. Bat when a thin section of it is
submitted to the microscope, it is seen that
this fibrous appearance is due to a peculiar
structure in the dentine, which the unaided
eye cannot discover. The dentinal sub-
stance is itself very transparent; but it is
traversed by minute tubuli, which appear
as dark lines, generally in very close ap-
proximation, running from the internal por-
tion of the tooth towards the surface, and
exhibiting numerous minute undulations,
and sometimes more decided curvatures, in
their course. They occasionally divide
into two branches, which continue to run
at a little distance from one another in the same direction; and they
also frequently give off small lateral branches, which again sencl off"
smaller ones. In some animals, the tubuli may be traced at their
extremities into minute cells, or cavities, analogous to the lacunae
of bone ; and the lateral branchlets occasionally terminate in such
cavities, which are called the intertubular cells. The diameter of
the tubuli at their largest part averages l-10,000th of an inch ; their
smallest branches are immeasurably fine. It is impossible that even
the largest of them can receive blood, as their diameter is far less-
than that of the blood-discs ; but it is probable that, like the canali*
culi of bone, they may absorb nutrient matter from the vascular sur~
face, with which their internal extremities are in relation.

312. In the Teeth of Man and of most Mammalia, we find the
central portion hollow ; and lined, in the living tooth, by a vascular
membrane. This cavity, with its vascular wall, is analogous to an
enlarged cancellus or Haversian canal of Bone ; and, as we shall pre-
sently see, it is formed in a similar manner. Upon the walls of the
cavity, all the tubuli open ; and they radiate from this towards the
surface of the upper part of the tooth, as shown in the accompanying-
figure. The central cavity is continued as a canal through each fang-
or root ; and the dentinal tubes in like manner radiate from this,,
towards the surface of the fang. — In the teeth of many of the lower
animals, however, we find a network of canals extending through the
substance of the tooth, instead of a single cavity; and these canals are

194 STRUCTURE AND DEVELOPMENT OF DENTINE.

frequently continuous with the Haversian canals of the subjacent bone,
so that the analogy between the two is complete. From each canal
the dentinal tubuli radiate, just in the manner of the canaliculi of bone
(§ 279); and thus we may regard a tooth of this kind as repeating, in
each of the parts surrounding one of these canals, the structure of the
human tooth.

313. The process by which the cellular mass, or pulp, of the dental
papilla, becomes converted into the dentine of the perfect tooth, is
thus described by Prof. Owen, from his investigations into the his-
tory of the Shark's dentition. — The pulp becomes vascular, by the
extension of the capillary network into its substance ; the vessels are
also accompanied by fine branches of nerves. The cells arrange
themselves in lines, radiating from the centre to the circumference of
the pulp ; and they become somewhat elongated in that direction. A
series of changes takes place in the nuclei of the cells, consisting
chiefly in their elongation and subdivision; so that they form a series
of parallel lines within each cell. The subdivided and elongated
nuclei become attached, by their extremities, to the corresponding
(nuclei of the cells in advance, and the attached extremities form con-
tinuous lines; so that in each row or file of cells, extending from the
inner part to the circumference of the pulp, there are several dark
lines, apparently continuous, which are formed by rows of granules
(or perhaps incipient cells) thus derived from the once single and
Tounded nuclei of the parent-cells. During the same time, the walls
«of the adjacent cells come into closer proximity, to the exclusion of
the gelatinous matter, that originally intervened between them ; and
they secrete calcareous matter, derived from the blood, into their own
cavities. The cells thus become completely filled with that material
(probably combined with gelatin, as in bone), excepting in the part
•occupied by the rows of granules, which are thus left unconsolidated;
and which, when the granules disappear at a subsequent period,
remain as the dentinal tubes. This consolidation first takes place on
the exterior of the pulp ; and the calcifying process gradually extends
itself inwards, causing the blood-vessels to retreat, as it were, towards
the centre, where an unconsolidated portion usually remains.

314. Thus the substance of the outer portion of the pulp is actually
•converted into dentine, and does not form it by a process of excretion,
as was formerly supposed. In general, the coalescence of the original
cells is so complete, that their boundaries altogether disappear, and
the substance that intervenes between the tubuli seems quite homo-
geneous; but distinct traces of the original division into cells may
•often be met with, in the dentine of Man (Fig. 50), as well as in that
of other animais ; which satisfactorily confirms what has been just
stated, as to the mode of its formation. Although in the most charac-
teristic form of Dentine, no blood-vessels exist, yet there are certain
«pecies, both among Mammals, Reptiles, and Fishes, in which the
Dentine is traversed by cylindrical prolongations of the central cavity,
•convejing blood-vessels into its substance ; and the presence of these

STRUCTURE AND DEVELOPMENT OF DENTINE. 195

medullary canals thus gives to the Dentine a vascular character ; and
thus increases its resemblance to bone. — The central portion of the
pulp is sometimes converted into a substance still more nearly resem-
bling bone, having its stellate lacunae as well as its vascular canals.
This change is normal or regular in certain animals, as in the extinct
Iguanodon and Icthosaurus, and in the Cachalot or Sperm-whale ; and
the ossified pulp bears a close resemblance to the bones of the respect-
ive animals, although it is not formed in continuity with them. A
similar change occurs in the Human tooth; — sometimes, it would
appear, rapidly, as the result of disease ; but in general more slowly,
increasing gradually with the advance of age.

315. It is not easy to ascertain the amount of nutritive change that
takes place in the substance of Dentine, when it is once fully formed.
When young animals are fed with colouring-matter, it is found to
tinge their teeth, as well as their bones ; and if the tooth be in process
of rapid formation at the time of the experiment, the progressive cal-
cification of the pulp, from without inwards, is marked by a series of
concentric lines. Even in the adult, some tinge will result from a
prolonged use of this substance ; and it has been noticed that the
teeth of persons, who have long suflTered from Jaundice, sometimes
acquire a tinge of bile. These facts show that, even after the com-
plete consolidation of the Dentine, it is still pervious to fluids: and
that in this manner it may draw into itself, from the vascular lining
of the pulp-cavity, a substance capable of repairing its structure, is
proved by the circumstance, that a new layer of hard matter is occa-
sionally thrown out upon a surface which has been laid bare by caries.

316. In those simple teeth which consist solely of Dentine, the
mode of production already described, — that of the consolidation of a
papilla upon the mucous membrane of the mouth, — is all which is
requisite. When the formation of the tooth itself is complete, it may
remain attached only to the mucous membrane, which is the case in
the Shark, or it may grow downwards, by the addition of new dental
structure at its base, until it comes in contact with the bone of the
jaw. Where it is only attached to the mucous membrane, as in the
Shark, it is very liable to be torn away ; but a new tooth, formed from
a distinct papilla, is ready to replace it; and this process is continually
repeated, the development of new papillae being apparently unlimited.
On the other hand, where the root of the tooth comes in contact with
the jaw, it may completely coalesce with it, which is the case in many
Fishes, the Haversian canals of the bone being continued as medullary
canals into the dentine ; or it may send long spreading roots into the
bone, which are united to it at their extremities. In the classes of
Fishes and Reptiles (with scarcely any exceptions) the teeth are by
no means permanent, as among Mammalia; but new teeth are con-
tinually succeeding the old ones. The mode in which these teeth
originate, by small buds from the capsules of the preceding, will be
understood when the capsular development of all the higher forms of
the dental apparatus has been described.

196

STRUCTURE OF ENAMEL.

317. It is obvious that there is no provision, in the simple calcifi-
cation of the dental papilla, for any variations or density, other than
those which may result from the different degrees of hardness in the
substance of the dentine itself. Now in the teeth of Man and most
other Mammals, and in those of many Reptiles and some Fishes, we
find two other substances, one of them harder, and the other softer,
than Dentine; the former is termed Enamel; and the latter Cementum
or Crusta petrosa. For the development of these, a peculiar modifi-
cation of the apparatus is requisite.

318. The Enamel is composed of long prismatic cells, exactly
resembling those of the prismatic shell-substance formerly described,
but on a for more minute scale ; the diameter of the cells not being
more, in Man, than l-5600th of an inch. The length of the prisms
corresponds with the thickness of the layer of enamel ; and the two
surfaces of this layer present the ends of the prisms, which are usually
more or less regularly hexagonal. The quantity of animal matter
in the tooth of the adult is extremely minute, — not above two parts
in 100 ; and it is only at a very early age, that the true character of
the animal structure can be distinctly seen. The course of the pris-
matic cells is more or less wavy ; and they

F'g-52. are marked by numerous transverse striae,

resembling those of the prismatic shell-sub-
stance, and probably originating in the same
cause, — the coalescence of a line of shorter
cells, to form the lengthened prism. No
trace of tubuli or of blood-vessels is to be
found in the completely formed Enamel of
higher animals ; but in the teeth of certain
Fishes, it is penetrated by calcigerous tubes,
which enter its substance from the exterior,
and ramify and subdivide like those of the
dentine. Of the 98 parts of mineral matter
in the enamel, 88^ consist (according to
Berzelius) of phosphate of lime, 8 of car-
bonate of lime, and IJ of phosphate of
magnesia. In density and resisting power,
the Enamel far surpasses any other organ-
ized tissue, and approaches some of the
hardest of mineral substances. In Man,
and in Carnivorous animals, it covers the
crown of the tooth only, with a simple cap
or superficial layer of tolerably uniform thickness (Fig. 52, 1),
which follows the surface of dentine in all its inequalities ; and its
component prisms are directed at right angles to that surface, their
inner extremities resting in slight but regular depressions on the exte-
rior of the dentine. In the teeth of many Herbivorous animals, how-
ever, the Enamel forms (with the Cementum) a series of vertical
plates, which dip down (as it were) into the substance of the dentine,

Vertical section of human mo-
lar tooih;— 1, enamel ; 2, cemen-
tum or crusta petrosa; 3. dentine
or ivory ; 4. osseous excrescence,
arising from hypertrophy of ce-
mentum; 5, cavity; 6, osseous
cells at outer pan of dentine.

CEMENTUM.— FORMATION OF DENTAL CAPSULE. 197

and present their edges alternately with it, at the grinding surface of
the tooth ; and there is in such teeth no continuous layer of dentine
over the crown. The purpose of this arrangement is evidently to
provide, by the unequal wear of these three substances, — of which
the Enamel is the hardest and the Cementum the softest, — for the
constant maintenance of a rough surface, adapted to triturate the
tough vegetable substances on which these animals feed. — The
Enamel is the least constant of the Dental tissues. It is more fre-
quently absent than present in the teeth of the class of Fishes ; it is
wanting in the entire order of Ophidia (Serpents) among existing
Reptiles ; and it forms no part of the teeth of the Edentata (Sloths,
&c.) and Cetacea (Whales) amongst Mammals.

319. The Cementum, or Crusta Petrosa, has the characters of true
bone ; possessing its distinctive stellate lacunae and radiating canali-
culi. Where it exists in small amount, we do not find it traversed by
medullary canals ; but, like Dentine, it is occasionally furnished with
them, and thus resembles Bone in every particular. These medullary
canals enter its substance from the exterior of the tooth ; and conse-
quently pass towards those, which radiate from the central cavity
towards the surface of the dentine, where it possesses a similar vas-
cularity,— as was remarkably the case in the teeth of the extinct
Megatherium. — In the Human tooth, however, the Cementum has no
such vascularity. It forms a thin layer, which envelops the root of
the tooth, commencing near the termination of the capping of Enamel
(Fig. 52, 2). This layer is very subject to have its thickness increased,
especially at the extremity of the fangs, by hypertrophy, resulting
from inflammation ; and sometimes large exostoses are thus formed
(Fig. 52, 4), which very much increase the difficulty of extracting the
tooth. When the tooth is first developed, the Cementum envelops
its crown, as well as its body and root ; but the layer is very thin
where it covers the Enamel, and being soft, it is soon worn away by
use. In the teeth of many Herbivorous Mammals, it dips down with
the Enamel to form the vertical plates of the interior of the tooth ; and
in the teeth of the Edentata as well as of many Reptiles and Fishes,
it forms a thick continuous envelop over the whole of the surface,
until worn away at the crown.

320. The development of these additional structures is provided
for by the enclosure of the primitive papilla, from which the Dentine
is formed, within a Capsule, which, at one period, completely covers
it in : between the inner surface of the capsule, and the outer surface
of the dentinal papilla, a sort of epithelium is developed, by the cal-
cification of which, the Enamel is formed ; and the Cementum is
generated by the conversion of the capsule itself into a bony sub-
stance.— The processes by which this capsular investment is pro-
duced, and the tooth completed and evolved, will now be briefly
described, as they occur in the Human foetus.

321. The dental papillae begin to make their appearance, at about
the seventh week of embryonic life, upon the mucous membrane

198 DEVELOPMENT OF HUMAN TEETH.

covering the bottom of a deep narrow groove (Fig. 53, a), that runs
alon^ the edge of the jaw (Fig. 53, b); and during the tenth week,
processes from the sides of this " primitive dental groove," particu-

Fig. 53.

Successive stages of the development of the deciduous or temporary teeth, and of the origin of the
sacs of the permanent set.

larly the external one, begin to approach one another, so as to divide
it, by their meeting, into a series of open follicles, at the bottom of
which the papillae may still be seen. At the thirteenth week, all the
follicles being completed, the papillae, which were at first round blunt
masses of cells, begin to assume forms more characteristic of the teeth
which are to be developed from them ; and by their rapid growth,
they protrude from the mouths of the follicles (Fig. 53, c). At the
same time, the edges of the follicles are lengthened into little valve-
like processes, or opercula, which are destined to meet and form
covers to the follicles (Fig. 53, d). There are two of these opercula
in the Incisive follicles, three for the Canines, and four or five for the
Molars. And by the fourteenth week, the two lips of the dental
groove meet over the mouths of the follicles, so as completely to
enclose each papilla in a distinct capsule (Fig, 53, e). At this period,
before the calcification of the primitive pulps commences, a provision
is made for the production of the second or permanent molars ; whose
capsules originate in buds or offsets from the upper part of the cap-
sules of the temporary or milk-teeth (Fig. 53,/). These offsets are
in the condition of open follicles, communicating with the cavity of
the primitive tooth ; but they are gradually closed in, and detached
altogether from the capsules of the milk-teeth (Fig. 53, g, A, i).

322. Soon after the closure of the follicles of the Milk-teeth, the
conversion of the cells of the original papilla into Dentine commences,
according to the method already described (§ 313). Whilst this is
going on, the follicles increase in size, so that a considerable space is
left between their inner w^alls and the surface of the dental papillae ;
which space is filled up with a gelatinous granular matter, the Enamel-
pulp. The portion of this which is converted into enamel, however,
is very small ; being only a thin layer, which is left on the inner sur-
face of the capsule after the remainder has disappeared. The interior
of the dental sac, at the time when the conversion-process has reached
the base of the dentinal pulp, is in the villous and vascular condition

DEVELOPMENT AND RENEWAL OF TEETH. 199

of a Mucous membrane, — which indeed it really is, having been, as
we have seen, once continuous with the lining of the mouth ; and the
layer of prismatic cells which covers its free surface, and by the cal-
cification of which the enamel is produced, may be regarded as an
epithelium. — The completion of the Enamel, and the ossification of
the capsule so as to form the Cementum, take place at a subsequent
period.

323. We have thus seen that the history of the first development
of the human teeth may be divided into three stages, the papillary,
the follicular, and the saccular. The papillary corresponds precisely
with the complete mode of dental development in the Shark and
other Fish, — as already mentioned. The follicular, which commences
with the enclosure of the papilla in open follicles, and terminates
when the papillae are completely hidden by the closure of the mouths
of those follicles, has also its permanent representation in the develop-
ment of the teeth of many Reptiles and Fishes ; the primitive papillae
of which, though enclosed in follicles, are never covered in at the
summit, and thus free themselves from their envelops by simply
growing upwards through their open mouths. But in Man, in all
other animals which agree with him in going on to the saccular stage,
there must also be an eruptive stage, which consists in the bursting-
forth of the tooth from the enclosing capsule ; the summit of the tooth
being carried against the lid of the sac, by the growth of its root (Fig.
53, h). By the continuance of the same growth, the teeth are caused
to penetrate the gum, and are gradually raised above its surface (Fig.
53, i).

324. All the permanent teeth, which are destined to replace the
temporary set, originate, as already stated, in buds or offsets from the
capsules of the latter. But behind the last temporary molars, which
are replaced by the permanent bicuspids, three permanent molars are
to be developed, on each side of either jaw. The Jlrst of these is
formed on precisely the same plan with the milk-teeth ; but is not
completed until a later period. The capsule of the second is formed
at a later period from that of the first, by a process of budding ex-
actly analogous to that by which the other permanent capsules are
formed from the corresponding temporary ; and at a still later period,
the capsule of the third permanent molar is formed as a bud from that
of the second. The evolution of this molar does not usually take
place until the system has acquired its full development ; and the
process of budding then ceases in Man, — being limited to a single
act of reproduction in the case of the ordinary Milk-teeth, and to a
double one in that of the first permanent Molar. In many animals of
the lower classes, however, the process goes on through the whole of
life without any limit; the newly-formed teeth, however, usually
replacing those of the previous set, and not being developed at their
sides like the second and third permanent molars of Man.

325. By a process of this kind, the continual renewal of the Teeth
takes place in those Reptiles and Fishes, whose dentition goes on to

200

DEVELOPMENT AND SUCCESSION OF TEETH.

the saccular stage ; in those at which it stops at the papillary, the
successive teeth are formed from new and independent papillae. The
only exception to the rule, that no Reptiles or Fishes have permanent
teeth, is found in the curious Dicynodon ; an extinct Reptile which
had two large tusks growing from persistent pulps, like those of the
Elephant, the front teeth of the Rodentia, and the grinders of the
Edentata. In such teeth, the base of the pulp remains unconverted,
and a new development of cells is continually taking place in that
situation ; these new cells are in their turn converted into dentine, in
continuity with that previously formed ; and thus the toolh or tusk is
continually lengthening at its base, in a degree which compensates for
its usual wear at its summit. If anything should prevent that wear,
— as when the opposite tooth has been broken off, — there is an abso-
lute increase in the length of the tooth, from the continued growth at
its base ; which may become a source of great inconvenience to the
animal. There is nothing, in the human subject, at all analogous to
this mode of development from persistent pulps ; the process being
checked by the closure of the root around the base of the pulp, which
obstructs the supply of blood it receives. The analogy between the
continued succession of teeth in the lower Vertebrata, by the gem-
miparous reproduction of their capsules, and the development of the
capsules of the permanent teeth of Man from those of the temporary
set, is made further evident by the fact, that a third set occasionally
makes its appearance in persons advanced in life ; the development
of which would not be intelligible, if we could not refer it to the
continuance of the same process in the other capsules, as that which
regularly takes place to a limited extent in the permanent molars of
Man, and which goes on without limit through the whole lives of the
lower Vertebrata.

326. The following table shows the usual periods at which the
different teeth of the two sets first show themselves above the gum.
It must be borne in mind, however, that these periods are subject to
very great variation; and that the average alone can therefore be
expressed.

Temporary or

Deciduous Teeth.

Permanent Teeth,

Months.

Years.

Central Incisors

. • 7

First Molar . 6J to 7

Lateral Incisors

. 8—10

Central Incisors . 7 — 8

Anterior Molars

. 12—13

Lateral Incisors . 8 — 9

Canines

. 14—20

First Bicuspid . 9 —10

Posterior Molars

. 18—36

Second Bicuspid . 10 — 11
Canines . . 12 — 12J
Second Molars . 12J— 14
Third Molars . 16 —30

327. We have seen that the Teeth are formed, in the first instance,
upon the surface of the Mucous membrane of the mouth ; and con-

STRUCTURE AND DEVELOPMENT OF HAIR. 201

sequently they really form a part of the external or dermo-skeleton,
and not of the internal or osseous skeleton. They correspond, there-
fore, with the external skeletons of the Invertebrata ; and thus the
analogy which has been pointed out, between the enamel of teeth
and the prismatic cellular substance of the shells of Mollusca, and
between the dentine and the shells of the higher Crustacea, holds
good also in regard to the situation of these structures. Although the
teeth are the only ossified portions of the dermo-skeleton in Man, we
find the body partially or completely enclosed in an armour of bony
scales or plates, in certain Mammalia, Reptiles, and Fishes ; and in
some species of the last-named class, which have now ceased to exist,
the scales seem to have had the texture of Enamel.

328. In connection with the teeth, the structure and development
of the Hair may be described ; this substance being generated very
much in the same manner as dentine, — by the conversion of a pulp
enclosed in a follicle ; though the product of the transformation is
different. The Hair-follicle is formed by the inversion of the Skin,
as the Tooth-follicle is by an inversion of the Mucous membrane ;
and it is lined by a continuation of the epidermis. From the bottom
of the follicle, a sort of papilla rises up, formed of cells ; the exterior
of this, which is the densest part, is known as the bulb ; whilst the
softer interior is termed the pulp. The follicle itself is extremely
vascular ; and even the bulb is reddened by. a minute injection ;
though no distinct vessels can be traced into it. — It has been imag-
ined until recently, that the Hair, like the other extra-vascular tissues,
is a mere product of secretion ; its material, which is chiefly horny
matter of the same composition with that of the epidermis and its
other appendages (§227), being elaborated from the surface of the
pulp. This, however, proves to be a very erroneous account of it ;
as is shown by the results of recent microscopic inquiries into its
structure. Although the Hairs of different animals vary considerably
in the appearances they present, we may generally distinguish in them
two elementary parts ; — a cortical or investing substance, of a fibrous
horny texture ; and a medullary or pith-like substance, occupying
the interior. In some instances, however, there is scarcely any me-
dullary substance to be traced ; whilst in other cases (as in the hair
of the Musk-Deer) the entire hair seems made up of it.

329. The fullest development of both substances is to be found in
the spiny hairs of the Hedgehog, and in the quills of the Porcupine,
which are but hairs on a magnified scale. The cortical substance
forms a dense horny tube, to which the firmness of the structure seems
chiefly due ; whilst the medullary substance is composed of an aggre-
gation of very large cells, which seem not to possess any fluid con-
tents in the part of the hair that is completely formed. In the hair of
the Mouse and other small Rodents, we see the horny tube crossed
at intervals by partitions, which are sometimes complete, sometimes
only partial ; these are the walls of the single or double line of cells,
of which the medullary substance is made up. In the Human hair,

202 STRUCTURE AND DEVELOPMENT OF HAIR.

the chief part is composed of a tube of a horny substance, correspond-
ing with the cortical sheath of the hairs of other animals ; this is
fibrous in its texture, as may be shown by crushing the hair, after it
has been softened by maceration in dilute acid ; and the outlines of
the fibres are indicated by very delicate longitudinal striae, which
may be traced through its whole thickness. This fibrous structure
sometimes makes up the whole thickness of the hair ; but there is
usually a central medulla, composed of colourless cells, with which
pigment-cells are mingled. The hair is invested by a series of very
minute scales, resembling those of the epidermis, but much smaller;
these are arranged in rows, like tiles upon a roof, and their edges
form delicate lines upon the surface of the hair, which are sometimes
transverse, sometimes oblique, sometimes apparently spiral. The
colouring matter of the hair appears to be related to Haematosine ; it
is bleached by Chlorine ; and its hue seems dependent in part upon
the presence of iron, which is found in larger proportion in dark than
in light hair.

330. The fibres of the cortical substance are probably cells, which
have become elongated by the process formerly described, and which
have at the same time secreted horny matter into their interior. This
change is continually going on in the bulb of the hair, at the base of
the part previously completed ; and by the progressive formation of
new cells in the bulb, a constant growth of the cortical substance is
provided for. The mode in which the medullary substance is gene-
rated, does not seem very clear ; but it probably consists of the con-
tents of the cells of the pulp, in which a continuous growth goes on,
at the same rate with that of the bulb. Thus the Hair is constantly
undergoing elongation by the addition of new substance at its base;
precisely in the same manner as the teeth of certain Mammals grow
from persistent pulps. The part once formed usually undergoes no
subsequent alteration ; but there is evidence that it may be affected
by changes at its base, the effect of which is propagated along its
whole extent. Thus it is well known that cases are not unfrequent,
in which, under the influence of strong mental emotion, the whole of
the hair has been turned to gray, or even to a silvery white, in the
course of a single night ; — a change which can scarcely be accounted
for in any other way, than by supposing that a fluid, capable of che-
mically affecting the colour, is secreted at the base of the hair, and
transmitted by imbibition through the medullary substance to the
opposite extremity. The knowledge of the organized structure of
hair, enables us better to understand some of the effects of disease ;
and especially of that peculiar affection termed Plica Polonica. The
hair of individuals suffering from it is disposed to split into fibres,
often at a considerable distance from the roots, and to exude a glu-
tinous substance ; and these two causes unite in occasioning that
peculiar matting of the hair, which has given origin to the name of
the disease. In the hair thus affected, there is evidently a power
of transmitting fluid absorbed at the roots; and it is said that even

OF CELLS COALESCED INTO TUBES. 203

blood exudes from the stumps, when the hairs are cut off close to the
skin.

6. Of Cells coalesced into Tubes ^ with Secondary Deposit,

331. Most of the tissues which have been hitherto described, differ
in no essentiaLparticulars from those of Plants; the chief departure
from the forms presented by the latter, being in the Fibrous tissues,
which, as already observed, are introduced for the sake of facilitating
the movements of the several parts of the structure, one upon the
other. The various cellular tissues find their exact representatives
in those of the Vegetable fabric ; and the denser parts of the Animal,
such as Bone, Cartilage, &c., are represented by the solid substances
formed by the Plant in the heart-wood of the stem, the stone of fruits,
&c., — these substances acquiring their density in precisely the same
manner with the Osseous tissues, by the secreting action of their own
cells, which draw a solidifying material from the general circulating
fluid. But we now come to two tissues of the highest importance in
the Animal fabric ; the presence of which is, indeed, its distinguishing
characteristic. These are the Muscular, and the J^ervous tissues.
The former is the one, by which all the sensible movements of the
body are effected ; and the latter serves as the instrument, by which
sensations are received, and by which the will excites the muscles to
action, — besides serving as the medium for other operations, in which
motion is produced, without the intervention of either sensation or
will. These tissues, with the apparatus of bones and joints on which
the muscles act, constitute the purely animal portion of the fabric ;
and if a being could be constructed, in which they should befiapable
of continued activity without any other assistance, it would be in all
essential particulars an Animal. But, as we shall presently see, the
plans on which these tissues are formed, in fact the very conditions
of their existence and activity, are such, that they require constant
nutrition and re-formation; so that the Animal cannot exist, without
an apparatus for preparing, circulating, and maintaining in constant
purity, a fluid, by which nutrient operations may be effected, and
which shall also be the means of carrying off the products of the waste
consequent upon the action of those tissues. This apparatus consti-
tutes the Vegetative portion of the frame ; the elementary parts con-
cerned in which have been already noticed.

332. When we examine an ordinary Muscle with the naked eye,
we observe that it is made up of a number oi fasciculi or bundles of
fibres ; which are arranged side by side with great regularity, in the
direction in which the muscle is to act ; and which are united by
areolar tissue. These fasciculi may be separated into smaller parts,
which appear like simple fibres ; but when these are examined by
the microscope, they are found to be themselves fasciculi composed of
minuter fibres bound together by delicate filaments of areolar tissue.
By carefully separating these, w^e may obtain the ultimate Muscular

204

STRUCTURE OF MUSCULAR FIBRE.

Fig. 54.

Fasciculus
striated Muscular
Fibre, showing at
a the transverse
striae, and at b, the
longitudinal striae,
more distinctly.

Fig. 55.

Fibre. This fibre exists under two forms, the striated and the no»-
striated; the former makes up the whole substance of
those muscles, over which the will has control, or
which are usually called into operation through the
nerves ; whilst the latter exists in the muscles which
the will cannot influence, and which are excited to
contraction by stimuli that act directly upon them.
The muscles of the former class minister to the ani-
mal functions ; those of the latter to the functions of
organic or vegetative life. The appearance presented
by the striated fibres of voluntary muscles, is shown
in Fig. 54 ; that of the non-striated fibres of the mus-
cles of organic life, in Fig. 55.

333. When the fibre of voluntary muscle is more
closely examined, it is seen to consist of a delicate
tubular sheath, quite distinct on the one hand from
the areolar tissue which binds the fibres into fasciculi,
and equally distinct from the internal substance of the
fibre. This cannot always be brought into view, on
account of its transparency ; it becomes most evident, when (as oc-
casionally happens) the contents of the fibre are separated transversely

by the drawing apart of its extremities,
without the rupture of the sheath ; but it
may also be sometimes seen rising up in
wrinkles upon the surface of the fibre, when
the latter is in a state of contraction. This
membranous tube, which has been termed
the Myolemma, has nothing to do with the
production of the striae ; these being due,
as will be presently shown, to the peculiar
arrangement of its contents. It is not per-
forated either by nerves or capillary vessels ;
and forms, in fact, a complete barrier be-
tween the real elements of Muscular struc-
ture, and the surrounding parts. That it
has no share in the contraction of the fibre,
is evident from the fact just mentioned, in
regard to its wrinkled aspect when the fibre
is shortened.

334. Although Muscular fibres are com-
monly described as cylindrical in form, yet
they are in reality rather polygonal, their
sides being flattened against those of the
adjoining fibres. In some instances, the angles are sharp and decided;
in others they are rounded oflf, so as to leave spaces between the con-
tiguous fibres, for the passage of vessels. In Insects, the fibres often
present the form of flattened bands, on which the transverse striae are
very beautifully marked. The size of the fibres is subject to great

Non-striated Muscular Fibre ; at
b, in its natural state ; at a, show-
ing the nuclei after the action of
acetic acid.

STRIATED MUSCULAR FIBRE.

205

Tariation, not merely in different classes of animals, but in different
species, in different sexes of the same species, and even in different
parts of the same muscle. Thus Mr. Bowman estimates the average
diameter of the fibres in the Human male at l-352d of an inch ; the
largest being l-192d, and the smallest l-507th. In the female, he
found the average to be 1 -454th of an inch ; whilst the largest was
l-384th, and the smallest 1-6 15th. The average size of the Mus-
cular fibre is greater among Reptiles and Fishes, than in other Verte-
brata ; but on the other hand the extremes are much wider. Thus
its dimensions vary in the Frog from 1-lOOth to 1-lOOOth of an inch ;
and in the Skate from l-65th to l-300th.

335. When the striated Muscular Fibre is examined still more
closely, it is found to contain an assemblage of very minute elements,
which appear to be flattened disk-like cells, of very uniform size.
These primitive particles are adherent to each other both by their flat
surfaces, and by their edges. The former adhesion is usually the
most powerful ; and causes

the substance of the fibre, Fig. 56.

when it is broken up, to
present itself in the form
of delicate Jihrillse, each of
which is composed of a
single row of the primitive
particles (Fig. 56). On the
other hand, the lateral ad-
hesion is sometimes the
stronger ; and causes the
fibre to break across into
disks, each of which is composed of a layer of the primitive particles
(Fig. 57). That the fibre is a solid collection of these elementary
parts, and not hollow in the centre, as some have supposed, is shown
by making a thin transverse section of a fasciculus (Fig. 58) ; by
which also the polygonal form of the fibre is made apparent.

Striated Muscular fibre separating into fibrillae, from a
preparation by Mr. Lealand.

Fig. 67.

Fig. 58.

An ultimate fibre, in which the transverse
splitting into disks, in the direction of the
striatiou of the ultimate fibrils, is seen.

Transverse section of ultimate fibres
of the biceps. In this figure the poly-
gonal form of the fibres is seen, and
their composition of ultimate fibrils.

206

STRIATED MUSCULAR FIBRE.

Fig. 39.

336. When the fibrillse are separately examined, under a high mag-
nifying power, they are seen to present a cylindrical or slightly-beaded
form, and to be made up of a linear aggregation of distinct cells. We
observe the same alternation of light and dark spaces, as when the
fibrillae are united into fibres or into small bundles; but it may be
distinctly seen, that each light space is divided by a transverse line ;
and that there is a pellucid border at the sides of the dark spaces, as
well as between their contiguous extremities (Fig. 59). This pellucid
border seems to be the cell-wall ; the dark space enclosed by it (which
is usually bright in the centre) being the cavity of the cell, which is
filled with a highly-refracting substance. When the fibril is in a
state of relaxation, as seen at a, the diameter of the
cells is greatest in the longitudinal direction : but
when it is contracted, the fibril increases in diameter
as it diminishes in length ; so that the transverse dia-
meter of each cell becomes equal to the longitudinal
diameter, as seen at b; or even exceeds it. Thus the
act of Muscular contraction seems to consist in a
change of form in the cells of the ultimate fibrillae,
consequent upon an attraction between the w^alls of
their two extremities ; and it is interesting to observe,
how very closely it thus corresponds with the contrac-
tion of certain Vegetable tissues, of which the com-
ponent cells (§ 345) appear to produce a movement,
when they are irritated, by means of a similar change
of form. The essential difference, therefore, between
the muscular tissue of Animals, and the contractile
tissues of Plants, consists in the subjection of the
former to nervous influence (§ 353). The diameter
of the ultimate fibrilltB will of course be subject to
variations, in accordance with their contracted or re-
laxed condition ; but seems to be otherwise tolerably
uniform in different animals, being for the most part
about 1-I0,000th of an inch. It has been observed,
however, as high as l-5000th of an inch, and as low
as l-20,000th, even when not put upon the stretch.
The average distance of the stricE, too, is nearly uniform in different
animals ; though considerable variations present themselves in every
individual, and in different parts of the same muscle. Thus the
maximum distance varies in different animals from 1- 15,000th to
l-20,000th of an inch ; the minimum from l-7500th to i-4500th of
an inch ; while the mean does not depart widely in any instance from
l-10,000th.

337. The Muscular fibre of Organic Life is very different from that
which has been now described. It consists of a series of filaments,
which do not present transverse markings; but which are tubular like
the preceding, their contents having a granular consistence, without

I

B

e

1

■

1

B

1

m

i

m
i

i

B

i

m

1

il

Structure of the
ultimate fibrillae
of striated muscu-
lar fibre :— a, a fi-
bril in a state of
ordinary relaxa-
tion ; h, a fibril in
a state of partial
contraction.

NON-STRIATED MUSCULAR FIBRE.

207

A. A muscular fibre of
organic life from the uri-
nary bladder, magnified
600 times, linear measure.
Two of the nuclei are
seen.

B. A muscular fibre of
organic life, from the sto-
mach, mjignified 600 times.
The diameter of this and
of the preceding fibre, mid-
way between the nuclei,
•was l-4750ih of an inch.

any definite arrangement of the particles into disks or fibrillse. Their
size is usually much less than that of the striated
muscular fibre ; but owing to the extreme varia-
tion in the degree of flattening which they undergo,
it is difficult to make even an average estimate of
their dimensions. Those of the alimentary canal
of Man are stated by Dr. Baly to measure from
about the l-2500th to the l-5600th part of an inch
in diameter. They generally present nodosities or
enlargements at frequent intervals (Fig. 60) ; the
character of which will be presently apparent.
These fibres are, like those of the other muscles,
arranged in a parallel manner into bands or fasci-
culi ; but these fasciculi are generally interwoven
into a network, without having any fixed points of
attachment. It is of this kind of structure, that
the proper muscular coat of the oesophagus, of the
stomach and intestinal canal, and of the bladder,
is composed ; it makes up, also, the substance of
the pregnant uterus : and it is found in no incon-
siderable amount in the trachea and bronchial
tubes. The fibres of the uterus somewhat diffier in
their aspect from those of other parts; being much broader at their
centre, and tapering off towards their extremities. In the Heart, a
mixture of the striated and non-striated fibres is found ; a modification
of the latter form of tissue exists in the middle coat of the arteries,
especially in the smaller branches; and fibres of the same kind are
interwoven wdth the other fibrous tissues in the substance of the skin,
and especially in the dartos, giving it a contractility which is mani-
fested under the influence of cold or of mental emotions, and thus
producing that general roughness and rigidity of the surface, which are
known as cutis anserina, and throwing the scrotum into wrinkles.

338. From the study of the early development of Muscular Fibre,
it appears that the Myolemma, or external transparent tube, is the
part first formed ; this being distinctly visible, long before any traces
of fibrillae can be observed in it. This tube takes origin, like the
straight ducts of Plants, in cells laid end to end ; the cavities of
which coalesce, by the disappearance of the partitions, at a subse-
quent period. The nuclei of these original cells may be distinctly
seen, for some time after the appearance of the transverse striae, which
indicate the formation of the fibrillae in their interior ; and they pro-
ject considerably from the sides of the fibres. In the fully-formed
muscle of animal life, however, they are not perceptible, except when
the fibre is treated with weak acid; the effect of w^hich is to render
the nuclei more opaque, whilst the surrounding structure becomes
more transparent. They are usually numerous in proportion to the
size of the fibre. There is every probability that these nuclei con-
tinue to act, like the " germinal spots" of the glandular follicles, as

208

DEVELOPMENT AND GROWTH OF MUSCULAR FIBRE.

Fig 61.

Mass of ultimate fibres from the
pectoralis major of the human
foetus, at nine months. Thtse
fibres have been immersed in a
solution of tartaric acid, and their
"numerous corpuscles, turned in
various directions, some present-
ing nucleoli," are shown.

centres of nutrition ; from which the minute cells that compose the
fibrillae are developed as they are required. The diameter of the
Muscular Fibre of the foetus is not above
one-third of that which it possesses in the
adult; and as the size of the ultimate par-
ticles is the same in both cases, their number
must be greatly multiplied during the growth
of the structure. But we shall find reason
to believe, that the decay of these particles
is constantly taking place, with a rapidity
proportional to the functional activity of the
Muscle ; and their generation, which occurs
as continually, when the nutrient operations
proceed in their regular course, is proba-
bly accomplished by a development from
these centres, at the expense of the blood
with which the Muscle is copiously sup-
plied.

339. From the preceding history it appears, that there is no dif-
ference, at an early stage of development, between the striated and
the non-striated forms of muscular fibre. Both are simple tubes,
containing a granular matter in which no definite arrangement can be
traced, and presenting enlargements occasioned by the presence of
the nuclei. But whilst the striated fibre goes on in its development,
until the fibrillae, with their alternation of light and dark spaces, are
fully produced, the non-striated fibre retains throughout life its ori-
ginal embryonic condition.

340. We have seen that the Muscular tissue, properly so called,
is as extra-vascular as cartilage or dentine ; for its fibres are not
penetrated by vessels ; and the nutriment required for the growth of
its contained matter is drawn by absorption through the myolemma.

But the substance of Muscle is extremely
vascular ; the capillary vessels being dis-
tributed in nearly parallel lines, in the
minute interspaces between the fibres;
so that it is probable that there is no
fibre, which is not in close relation with
a capillary. Hence there is every pro-
vision for the active nutrition of this
tissue; the arterial circulation bringing
the materials for its growth and renova-
tion ; whilst the venous conveys away
the products of the waste or disintegration, which is consequent upon
its active exercise. The supply of blood is not merely requisite for
the nutrition of the muscular tissue ; but it also affords a condition
which is requisite for its action. This condition is oxygen. It is not
enough that blood should circulate through the muscles; for that
blood, to exercise any beneficial influence, must be arterialized.

Capillary network of Muscle.

NUTRITION AND COMPOSITION OF MUSCLE. 209

Consequently the muscles of warm-blooded animals soon lose their
contractile power, after the supply of arterial blood has been sus-
pended, either by the cessation of the circulation, or by the want of
aeration of the blood ; but those of cold-blooded animals preserve
their properties for a much longer period, in accordance with the
general principle formerly stated, — that, the lower the usual amount
of vital energy, the longer is its persistence, after the withdrawal of
the conditions on which it is dependent.

341. The Muscles of Animal Life are, of all the tissues except the
Skin, the most copiously supplied with Nerves. These, like the blood-
vessels, lie on the outside of the Myolemma of each fibre ; and their
influence must consequently be exerted through it. The arrangement
of these nerves is shown in the succeeding figure. Their ultimate
fibres or tubes cannot be said to terminate anywhere in the muscular
substance ; for after issuing from the trunks, they form a series of
loops, which either return to the same trunk, or join an adjacent one.
The occasional appearance of a termination to a nervous fibril is
caused by its dipping-down between the muscular fibres, to pass
towards another stratum. — The non-striated muscles, however, are
very sparingly supplied with nerves ; and these are derived, — for the
most part, if not entirely, — from the Sympathetic system, rather than
from the Cerebro-spinal.

342. Every Muscular Fibre, of the striated kind at least, is at-
tached at its extremities to fibrous tissue ; through the medium of
which it exerts its contractile power on the bone or other substance,
which it is destined to move. The muscular fibre usually ends ab-
ruptly by a perfect disk ; and the myolemma seems to terminate there.
The tendinous fibres are attached to the whole surface of the disk ;

Fig. 63.

Portion of muscle, showing the arrangement of the motor nerves supplying it.

and probably become continuous with the myolemma. Thus the-
whole muscle is penetrated by minute fasciculi of tendinous fibres ;
and these collect at its extremities into a tendon. Sometimes the
14

210 CONTRACTILITY OF VEGETABLE TISSUES.

muscular fibres are attached obliquely to the tendon, which forms a
broad band that does not subdivide; this is seen in the legs of Insects
and Crustacea, in which the muscular fibres have what is called a
joenwi/brm arrangement, being inserted into the tendon, on either side,
like the laminse of a feather into its stem. — The forms which diflferent
muscles present, have reference purely to the mechanical purposes,
which they have respectively to accomplish. The elements are the
same in all, both as regards structure and properties.

343. Notwithstanding the energy of growth in Muscular tissue, it
is doubtful if it is ever regenerated, when there has been actual loss
of substance. Wounds of muscles are united by Areolar Tissue,
which gradually becomes condensed; but its fibres never acquire
any degree of contractility.

344. It is probable that the pure Muscular Fibre is identical in
Chemical composition, — or nearly so, — with the Fibrin of the blood.
It is, however, impossible to separate it completely from the areolar
tissue, nerves, blood-vessels, fatty matter, &c., which enter into the
substance of the muscle ; so that it cannot be precisely analyzed. In
ordinary muscle, the solid matter forms about 23 parts in 100 ; the
remainder consisting of water. — The solid matter contains about 7^
per cent, of fixed salts.

345. We now come to investigate the remarkable property, which
is the distinguishing characteristic of Muscular tissue; — that of con-
tracting on the application of a stimulus. Some approaches to this
property are manifested by certain Vegetable structures. Thus, if
the small enlargement at the base of the footstalk of the leaf of the
Sensitive Plant, be touched ever so slightly, the leaf will be imme-
diately drawn down by the contraction of the tissue of the part
irritated. If the leaf itself be touched, the same effect results, but
apparently through a different channel ; the tissue of the leaf contracts
where it is touched, and forces some of its fluid along the vessels of
the footstalk into the upper side of the little excrescence at its base,
by the distension of which the leaf is forced down. In the IHoncea
muscipula, or Venus's Fly-trap, there is a similar transmission of the
effect of the stimulus from one part to another ; for the two lobes of
the leaf, which form the trap, are made to close together, when an
insect settles upon either one of three spines which project from the
surface of each lobe, or when the points of these spines are touched
with any hard body. Many other instances of Vegetable movement
might be brought together. Some of them are obviously produced
by an enlargement or contraction of the cells, occasioned by variations
in the amount of fluid they contain ; and these variations depend upon
the hygrometric state of the atmosphere. With these we have nothing
to do. But there are many, in which (as in the case of the Sensitive-
plant first mentioned) a stimulus applied to a part occasions the imme-
diate contraction of its cells, and a consequent motion in the same
part. And there are also several, in which the contraction produces
motion in a distant part, as in the Dionaea; but this propagation

INHERENT CONTRACTILITY OF MUSCULAR FIBRE. 211

appears to be of a simply mechanical character ; being accomplished
through the medium of fluid, which is forced from one part by its own
contraction, and caused to distend another.

346. From these examples, however, it is evident that the property
of contractility is not entirely restricted to the Animal kingdom ; and
we shall find that the simplest form under which it manifests itself in
the Animal body, bears a close relationship with that which is dis-
played in Plants. The non-striated fibre of the alimentary canal,
which is subservient to the functions of Vegetative life alone, is called
into action much more readily by a stimulus directly applied to itself,
than it is in any other mode. Such is not the case, however, with
the striated fibre, of which the muscles of Animal life are composed ;
this being much more readily called into action by a peculiar stimulus
conveyed through the nerves supplying those muscles, than in any
other more directly applied to them.

347. The Contractility of Muscular Fibre shows itself under two
forms. Its most obvious and striking manifestations are those that
occur in the voluntary muscles and in the heart ; which, when in
action, exhibit powerful contractions alternating with relaxations. The
property w^hich is concerned in these is distinguished as Irritability.
On the other hand, we find that these same muscles exhibit a tend-
ency to a moderate and permanent contraction, which is not shown
by them when they are dead, and which cannot, therefore, be the
result of elasticity or of any simple physical property ; this endow-
ment, which seems to exist in the greatest amount in certain forms of
the non-striated fibre, is called Tonicity.

348. That the irritability of Muscles is a property inherent in them,
and in this respect analogous to the peculiar vital endowments of any-
other forms of tissue, cannot be any longer a matter of doubt ; — though
many Physiologists have sought to show, that it is in some way
derived from the nerves. Not only may an entire Muscle be made
to contract, by the application of a proper stimulus, long after the
division of the nervous trunks supplying it; but even a single fibre,
completely isolated from all its nervous connections, may be seen to
contract under the Microscope. Moreover, in the non-striated mus-
cular fibre, it is often diflficult to excite contractions through the nerves
at all, when a stimulus directly applied to itself will immediately pro-
duce sensible and vigorous movements. The energy of the contractile
power depends in great part upon the state of nutrition of the muscle ;
and this again is influenced by the degree in which it is exercised.
Now as the Muscles of Animal Life are all excited to action, in the
usual state of things, through the medium of their nerves, it follows
that if the nerves be paralyzed, the muscles will be seldom or never
called into use. When disused, they will receive very little nourish-
ment; the disintegrating changes will not be counterbalanced by
reparative processes ; and in consequence, the muscular structure will
be gradually so far impaired, as to lose its peculiar properties, — and
will even, in time, almost totally disappear. Yet even after the

212 INHERENT CONTRACTILITY OF MUSCULAR FIBRE.

almost complete departure of muscular contractility, through the
metamorphosis of the structure consequent upon disuse, it may be
again recovered, if the muscles be called into exercise; but the
recovery of the power is very slow, and proceeds pari passu with the
improvement in the nutrition of the part, being more tedious in pro-
portion to the length of the previous disuse.

349. That the Irritability of Muscular fibre belongs to itself, and
is not derived in any way from the nerves, is further shown in the
following manner. If a set of muscles (as those of the leg of a Rabbit
or Frog) be repeatedly thrown into action by galvanism, until the
stimulus will no longer occasion their contraction, their irritability is
then said to be exhausted ; by rest, however, it is recovered, — the
nutritive processes making good the loss previously suffered. Now
it has been shown by Dr. J. Reid, that this recovery may take place,
even after the division of all the nerves supplying the limb ; provided
that the nutrition of the part be not interfered with. It has been
further shown by the same excellent Physiologist, that, if the nerves
of a limb be divided, the loss or retention of the contractility of the
muscles entirely depends upon the degree of exercise to which they
are subjected, and consequently upon the nutrition they receive.
The muscles of the hind-leg of a Rabbit, whose sciatic nerve had
been divided, were found to lose their contractility almost completely
in the course of seven weeks. They were much smaller, paler, and
softer, than the corresponding muscles of the opposite leg ; and they
scarcely weighed more than half as much as the latter. Now when
the nerves of both hind-legs of a Frog were cut, and the muscles of
one of the limbs thus paralyzed were daily exercised by a weak gal-
vanic battery, whilst those of the other were allowed to remain at
rest, it was found after the lapse of two months that the muscles of
the exercised limb retained their original size and firmness, and con-
tracted vigorously, whilst those of the other had shrunk to one-half
their former size. Though the latter still retained their contractility,
there could be no doubt that they would soon lose it, in consequence
of the change already far advanced in their physical structure ; this
change not being as rapid in cold-blooded animals, as in Birds and
Mammals.

350. By these and other facts, then, it may be regarded as com-
pletely proved, that the Irritability of Muscles is a vital endowment,
belonging to them in virtue of their peculiar structure ; — that, so long
as this structure is maintained in its normal condition by the nutritive
processes, so long is the property capable of being manifested ; — but
that any cause which interferes with the nutrition of a muscle, impairs
or destroys its irritability. No cause is so effectual in doing this, as
complete disuse; and no means is so sure to produce complete disuse
of a muscle, as the division of its nerve, since its being called into
exercise in any other way is very improl3able ; hence the section of
the nerve is almost certain to produce, in time, the loss of the con-
tractility of the muscle. But if a means be devised, by which the

I

EFFECTS OF STIMULI ON MUSCULAR FIBRE. 213

muscle may still be called into action in any other way, — as in Dr.
Reid's experiment just quoted, — its irritability is retained, because its
regular nutrition is continued.

351. We have now to inquire, then, into the circumstances under
which this peculiar endowment acts ; or the means by which it may
be called into operation, the mode in which the contraction takes
place, and the conditions which are necessary for its performance. —
All Muscular Fibre, which has not lost its contractility, may be made
to contract by a stimulus applied directly to itself; and this stimulus
may be of different kinds. The simplest is the contact of a solid sub-
stance ; thus we may excite muscular contractions by simply touching
the fibre, — ^just as we cause contraction in the tissue of the Dionsea
or Sensitive Plant. Most substances of strong chemical action, such
as acids and alkalies, will call forth the contractility of muscular fibre,
when applied to it ; and the same result is produced by heat, cold,
and electricity, — the last-named agent being the most powerful of
all. The effect of the application of any of these stimuli varies con-
siderably, according to the kind of Muscle on which it is exerted.
If we irritate a portion of a muscle composed of striated fibre (any
one of the voluntary muscles for example), the fasciculus of fibres
which is touched will immediately contract, and that one only ; and
the contracted fasciculus will soon relax, without communicating its
movement to any other.

352. If we irritate a portion of non-striated fibre, however, as that
of the Alimentary canal, the fasciculus which is stimulated will con-
tract less suddenly, but ultimately to a greater amount ; its relation
will be less speedy ; and before it takes place, other fasciculi in the
neighbourhood begin to contract; their contraction propagates itself
to others ; and so on. In this manner, successive contractions and
relaxations maybe produced through a considerable part of the canal,
by a single prick with a scalpel; a sort of wave of contraction being
transmitted in the direction of its length, and being followed by relaxa-
tion. Again, in the Muscular structure of the Bladder and Uterus,
powerful contractions are excited by irritation, and these produce a
great degree of shortening ; but they do not alternate in the healthy
state with any rapid and decided elongation ; whilst, on the other
hand, an irritation applied to one spot causes more extensive contrac-
tions than are seen to occur as its immediate consequence in the pre-
ceding cases. In the Heart, the muscular structure of a large part of
the organ is thrown into rapid and energetic contraction, by a stimu-
lus applied at any one point ; and this contraction is speedily followed
by relaxation. And in the fibrous tissue of the middle coat of the
Arteries, the contraction takes place rather after the manner of that
of the bladder and uterus, and a prolonged application of the stimulus
is often necessary to produce the effect ; but when the contraction
commences, it produces a considerable degree of shortening, which
takes place in other fasciculi than those directly irritated, and does not
speedily give way to relaxation.

214 ACT OF MUSCULAR CONTRACTION.

353. On the other hand, when the stimuli which excite muscular
contraction are applied to the nerve, which supplies a voluntary mus-
cle composed of striated fibre, they produce a simultaneous contraction
in the whole muscle; the effect of the stimulus being at once exerted,
upon every part of it. In the ordinary action of such muscles, the
nervous system is always the channel through which they are called
into play, whether to carry into effect the determinations of the mind
(§ 391), or to perform some office necessary to the continuance of
life, such as the movements concerned in Respiration (§ 394). The
nerves of the striated fibre are all derived at once from the brain or
spinal cord. — The ordinary actions of the non-striated fibre, on the
contrary, are executed in respondence to stimuli applied directly to
themselves. It is so difficult to excite contractions in it through the
medium of its nerves, that many Physiologists have denied the possi-
bility of doing so ; and the nerves lose their power of conveying the
influence of stimuli very soon after death, although the contractility
of the muscles may remain for a considerable time. The nerves of
the non-striated fibre are chiefly those belonging to the Sympathetic
system; but, as will be shown hereafter (Chap. XII.), those which
excite motion are probably derived in reality from the Cerebro-spinal
system, through the communicating branches which unite the two.

354. When a Muscle is thrown into contraction, its bulk does not
appear to be at all affected. Its extremities approach, so that it is
shortened in the direction of its fibres; but its diameter enlarges in
the same proportion. It was formerly supposed that the ultimate
fibreSj^in the act of contraction, threw themselves into zigzag folds;
but this is now well ascertained not to be the case. The fibre, like
the entire muscle, preserves its straight direction in shortening, and
increases in diameter. The fibrillse themselves, as already mentioned
(§ 336) exhibit an evident change, in regard to the distances of their
successive light and dark portions; and the fibre, which is made up
of these, exhibits, in its contracted state, a very close approximation
of the transverse striae; to such an extent that they become two, three,
or even four times as numerous in a given length, as they are in a
similar length of a non-contracted fibre. According to Mr. Bowman's
observations, the contraction usually commences at the extremities of
a fibre ; but it may occur also at one or more intermediate points.
The first appearance of contraction is a dark spot, caused by the ap-
proximation of the strise ; and this gradually extends itself, so as to
involve a greater or less proportion of the length of the fibre. The
approximation of the solid portions forces out the fluid, which was
previously contained amongst the fibrillse ; and this is seen to lie in
bullse or blebs beneath the myolemma, which is drawn up into
wrinkles.

355. The successive stages of the act of contraction can only be
thus observed, when it takes place very slowly, as in the rigor mortis^
or slow contraction after death, the phenomena of which will be pre-
sently noticed. But the resulting change in muscular fibres, which

ACT AND CONDITIONS OF MUSCULAR CONTRACTION. 215

have been made to contract by galvanism or any other stimulus, is
essentially the same. This may be best seen in transparent Entozoa,
Crustacea, and others among the lower Articulated Animals, whilst
alive. Again, in persons who have died from Tetanus, a considerable
number of the fibres are found to have been ruptured by the violent
spasmodic action ; the contractile force, called into action by the pow-
erful stimulation of the nerves, having overcome the tenacity of the
fibre : and in such cases, the same approximation of the transverse
striae, and proportional increase in the diameter of the fibre, are to be
observed.

356. It appears that, even when considerable force of contraction
is being exerted, the whole fibre is seldom or never in contraction at
once; but that a continual interchange is taking place amongst its
different parts, — some of them passing from the contracted to the
relaxed state, as shown by the separation of the transverse striae, —
whilst others are taking up the duty, and passing from the relaxed to
the contracted condition, as shown by the approximation of the striae.
But it is not only among the different parts of the individual fibres,
that this interchange seems to take place. There is good reason to
believe that, when a muscle is kept in a contracted state, by an effort
of the will, for any length of time, only a part of its fibres are in con-
traction at any one time ; but that a constant interchange of condition
takes place amongst them, some contracting whilst others are relaxing,
so that the entire muscle remains contracted, whilst the state of every
individual fibre may have undergone a succession of alterations.
When the ear is applied to a muscle in vigorous action, an exceed-
ingly rapid faint silvery vibration is heard, which seems to be attri-
butable to this constant movement in its substance.

357. Thus it appears that the prolongation of the contraction of a
muscle, through any length of time, is not opposed to the fact that, in
the individual fibres, relaxation speedily follows contraction ; but is
only a peculiar manifestation of it. The ordinary movements of the
Heart exhibit a different manifestation ; its fibres contracting simulta-
neously, and relaxing together, instead of alternating amongst them-
selves like those of a voluntary muscle. — The occasional zigzag
arrangement of the fibres, which has been supposed to be their con-
tracted state, is really dependent upon the approximation of their
extremities, in consequence of the contraction of some neighbouring
fibres, whilst their own condition is that of relaxation. It may be
artificially produced by bringing together the two extremities of a
fasciculus, after the irritability of the fibre has ceased ; so that the
flexure at determinate points must be owing simply to the physical
arrangement of the parts, — perhaps to the passage of nerves or ves-
sels in a transverse direction.

358. We have now to consider the conditions, which are requisite
for the manifestation of Muscular Irritability. It has been already
pointed out, how close is the dependence of the property upon the due
nutrition of the tissue ; but the property cannot be long exercised ex-

216 DEPENDENCE OF MUSCULAR CONTRACTION UPON OXYGEN.

cept under another condition, which is consequently of almost equal
importance, — the circulation of arterial blood through the substance
of the muscle. The length of time during which the contractility
remains, after the circulation has ceased, has been shown by Dr. M.
Hall to vary inversely to the activity of the respiration of the animal.
Thus in cold-blooded animals, the standard of whose respiration is
low, the contractility remains for many hours after death, even in the
voluntary muscles ; and the muscles of organic life retain it with
great tenacity. Thus the heart of a Frog will go on pulsating for
many hours after its removal frop the body ; and the heart of a Stur-
geon, which had been inflated with air and hung up to dry, has been
seen to continue beating, until the auricle had become absolutely so
dry, as to rustle during its movements. An exceedingly feeble Gal-
vanic current is sufficient to excite the muscles of these animals to
contraction ; so that Matteuci, in his experiments upon Animal Elec-
tricity, has been accustomed to use the prepared hind-leg of a Frog
as the best indicator of the passage of an electric current. Among
warm-blooded animals, the same rule holds good, in regard to the
inverse proportion of the duration of irritability, and the amount of
respiration ; for the muscles of Birds lose this property at an earlier
period after the cessation of the circulation, than do those of Mammals.
From experiments on the bodies of executed criminals, who were pre-
viously in good health, Nysten ascertained that, in the human subject,
the contractility of the several muscular structures, as tested by Galva-
nism, departs in the following time and order : — the left ventricle of the
heart first; the intestinal canal at the end of 45 or 55 minutes; the
urinary bladder nearly at the same time ; the right ventricle after the
lapse of an hour ; the oesophagus at the expiration of an hour and a
half; the iris a quarter of an hour later; and lastly, the ventricles of
the heart, especially the right, which in one instance contracted 16J
hours after death.

359. That the circulation of arterial or oxygenated blood through
the muscles, is the essential condition of the continuance of their irrita-
bility, appears from this, — that after the general death of the system,
and even after the removal of the brain and spinal cord, the muscles
will preserve their irritability, and the action of the heart itself will
continue for a long time, provided that the circulation be kept up
through the lungs by artificial respiration, on the principles hereafter
to be explained. (§ 688.) But if, whilst the general circulation
continues, the circulation through a particular muscular part be inter-
rupted, that organ will lose its contractility earlier than usual. Thus
it has been shown by Mr. Erichsen, that, if the coronary arteries
(supplying the substance of the heart) be tied in a dog or a rabbit,
after the animal has been pithed, and the circulation is being main-
tained by artificial respiration, the pulsation of the heart will only go
on for about 23 minutes after the ligature has been applied, or about
33 minutes after the death of the animal ; instead of continuing for 90
minutes, which it will do under other circumstances. Further, if blood

DISINTEGRATION OF MUSCLE BY USE. 217

charged with carbonic acid, instead of with oxygen, circulate through
the muscles, their irritability is speedily impaired, and is even de-
stroyed. This is best seen, when animals are killed by being caused
to breathe an atmosphere highly charged with carbonic acid ; the irri-
tability of their muscles departing as soon as they are dead. In fact,
the destruction of the irritability of the heart, by the circulation of
venous blood through its substance, is one of the immediate causes of
death. A similar effect is produced by the respiration of other gases,
which are either poisonous in themselves, or which prevent the inter-
change of carbonic acid and oxygen, which ought to take place in the
lungs. On the other hand, when animals have been made to respire
oxygen, and their blood has been consequently highly arterialized,
the contractility of their muscles is retained for a longer time than
usual.

360. Hence we may conclude the presence of oxygen in the blood
to be one of the conditions of muscular contraction; although it is
much less essential in the case of cold-blooded, than in that of warm-
blooded animals. It is interesting to remark,* that the muscles of %-
bernating warm-blooded Mammals are reduced for a time to the level
of those of cold-blooded animals ; their contractility being retained
almost as long as that of the latter ; thus confirming the general prin-
ciple already stated as to the relation between the amount of respira-
tion, and the duration of the irritability.

361. The Muscles, as we have seen, are largely supplied with
blood ; and the flow of blood into them increases with the use that is
made of them. The demand for nutrition is obviously augmented, in
proportion to the activity of the exercise of the Muscular system ; for
the slightest observation suffices to show, that a much smaller am ount
of nourishment is sufficient to sustain the body in its normal condition,
when the Muscular system is not actively exercised, than when it is in
energetic operation. The quantity w^hich is ample for an individual
leading an inactive life, is far too little for the same person in the full
exercise of his muscular powers. Again, there is evidence derived
from observation of the relative amount of the solid matters excreted
from the body under different circumstances, that a waste or disintegra-
tion of the muscular tissue takes place, whenever it is actively em-
ployed ; and this in a degree strictly proportional to the amount of force
which it is called upon to exercise. In fact, it would appear that this
waste is a necessary consequence of the exercise of the muscle ;■ — every
act of contraction involving the death and decomposition of a certain
amount of tissue. And as the presence of oxygen is always necessary
for the decomposition of organic substances, so do we find that the
penetration of the muscular tissue by oxygenated blood is essential to
the manifestation of its contractile power.

362. Every act of contraction, then, may be said to involve the
death of a certain amount of muscular tissue; and the products
of decomposition which consist of the elements of muscular fibre
united with the oxygen of the arterial blood, are carried off by the

218 DEPENDENCE OF IRRITABILITY UPON NUTRITION.

venous current. On the other hand, the muscular substance is re-
paired by an act of nutrition, at the expense of the fibrin supplied to
it by the circulating fluid. There are certain muscles, as the heart,
and the muscles of respiration, whose action is necessarily constant;
and their reparation must take place as unceasingly as their waste. In
these muscles no sense of fatigue is ever experienced. But in the
muscles which are usually put in action by the will, this is not the case.
Any prolonged exertion of them induces fatigue ; and this fatigue is
an evidence of their impaired condition, and of the necessity of rest
to impart to them a renewal of vigour. The rest of muscles is essen-
tial to the recovery of their powers ; and this recovery is due to the
nutritive operations, which then take place unchecked, and which
repair the losses previously sustained. The permanently increased
flow of blood to a muscle, which takes place when it is continually
being called into vigorous action, is thus on the one hand occasioned
by the demand for oxygenated blood created by its use, whilst on the
other hand it tends to increase the power of the muscle by an aug-
mentation of its nutrition. Hence it is, that the more a muscle is
exercised, the more vigorous and more bulky does it become. This
is equally the case whether the exercise of the muscle be voluntary
or not. We see examples of it in the arms of the smith and in the
legs of the opera dancer ; and we have a still more striking manifesta-
tion of it in those cases, in which an obstruction to the exit of urine
through the urethra, has called for increased efforts on the part of the
bladder, the continuance of which gives rise to an extraordinary aug-
mentation in the thickness of its muscular coat.

363. Thus we see that the property of Irritability is a vital endow-
ment peculiar to muscular tissue, and dependent for its existence upon
due nutrition of that tissue ; that it may be called into exercise by cer-
tain stimuli, applied either to the muscle itself, or to the nerve sup-
plying it, provided that the muscle be also permeated with oxygen ;
that it may be exhausted by repeated stimulation, but is then recov-
ered by rest, provided that there be no obstacle to the nutrition of
the muscle ; that the nutrition of the muscle is impaired by continued
repose, and that its irritability diminishes in the same proportion ; that
the nutrition is increased by frequent use, and that the power of the
muscle then augments in like degree ; and finally that the departure of
muscular power, which ensues upon the general death of the system,
is dependent in part upon the cessation of the supply of oxygen, and
in part upon changes in the composition of the muscle itself, which
are no longer compensated by the functions that keep it in its normal
condition during life. — The rapidity of these changes is the greatest
in warm-blooded animals, in which also the muscular irritability is
most dependent upon the presence of oxygen in the muscular sub-
stance ; consequently the irritability departs after death much more
speedily in these than in cold-blooded animals.

364. We have now to consider the other form of Contractility,
which produces a constant tendency to contraction in the Muscular

TONICITY OF MUSCLES.— RIGOR MORTIS. 219

fibre, but which is so far different from simple Elasticity, that it abates
after death, before decomposition has taken place. This Tonicity
manifests itself in the retraction which takes place in the ends of a
living muscle, when it is divided ; the retraction being permanent,
and greater than that of a dead muscle. It also shows itself in the
permanent flexure of joints, when, by paralysis of the extensors, the
tonic contraction of the flexors is not antagonized. In the healthy
state, it would seem as if the tonicity of the several groups of muscles
was so adjusted, as to be in mutual counterpoise ; but the balance is
destroyed when, in consequence of paralysis, or of impaired nutrition
from other causes, the tonicity of one set is weakened. This is the
case, for example, in the lead-palsy ; in which the extensors of the
forearm and hand lose their power, so that the tonic contraction of
the flexors keeps the fingers constantly bent upon the palm. It
would seem, however, that the tonicity of the flexors is usually greater
than that of the extensors ; as the former predominate, when all are
equally withdrawn from the control of the nervous system, in profound
sleep.

365. The Tonicity is much greater, relatively to the amount of
irritability, in the non-striated, than in the striated fibre ; and it is
particularly remarkable in the fibrous c^t of the arteries, in which it
is diflScult to procure any decided indication of irritability by the ap-
plication of stimuli. It is by this tonicity of the walls of the arteries,
that they are kept in a state of constant moderate contraction upon
their contents ; and that, when they are emptied, they contract until
the tube is nearly obliterated. If its amount be too great (as some-
times happens) the artery approaches the condition of a rigid tube ;
which, as will be shown hereafter, is unfavourable to the regularity
of the flow of blood through it, though the rate is increased. On the
other hand, if it be unduly diminished, the circulation is retarded,
by the tendency of the arterial walls to yield too much to the pulse-
wave.

366. This property is very greatly affected by temperature; being
diminished by w-armth, and increased by cold. Thus when an artery
is exposed to the air for some time, the lowering of its temperature
occasions its contraction to such an extent, that its tube may be almost
obliterated. And in the operation of crimping fish, immersion of the
body in cold water, after the muscles have been divided, increases
the tonic contraction of the muscles, and thus improves the firmness
to their substance, w^hich it is the object of this operation to produce.

367. The Rigor Mortis, or death-stiffening of the muscles, is pro-
bably to be regarded as a manifestation of this property, occurring
after all the Irritability of the muscles has departed, but before any
putrefactive change has commenced. This phenomenon is rarely
absent ; although it may be so slight, and may last for so short a time,
as to escape observation. The period which elapses before its com-
mencement is as variable as its duration ; and both seem to be de-
pendent upon the vital condition of the system at the time of death.

220 RIGOR MORTIS.

When it has been weakened or depressed by previous disease, the
irritability of the muscles speedily departs ; and the stiffening comes
on early, and lasts but a short time. Thus, after death from Typhus,
the limbs have been sometimes known to stiffen within 15 or 20
minutes. On the other hand, when the general vigour of the system
has not been previously impaired, and death has resulted from some
sudden cause, the irritability of the muscles is of longer duration,
and their stiffening is consequently deferred. The commencement of
the rigidity usually takes place within seven hours after death ; but
twenty or even thirty hours may elapse before it shows itself. Its
general duration is from twenty-four to thirty-six hours ; but it may
pass off much more rapidly, or it may be prolonged through several
days. It affects all the muscles composed of the striated fibre with
nearly the same intensity ; except that the flexors usually contract
more strongly than the extensors (as in sleep), the fingers being
closed upon the palm, the hand bending on the forearm, and the
lower jaw being drawn firmly against the upper. And it even mani-
fests itself in muscles that have been thrown out of use by paralysis,
provided that their nutrition has not been seriously impaired.

368. This tonic contraction, however, is most remarkably mani-
fested in the non-striated fibre ; and especially in the heart and blood-
vessels. As soon as the muscular walls of the several cavities lose
their irritability, they begin to contract forcibly upon their contents,
and thus become stiff and firm, although they were previously flaccid.
In this manner, the ventricles of the heart, which are the first parts
to lose their irritability, become rigid and contracted within an hour
or two after death; and usually remain in that state for ten or twelve
hours, sometimes for twenty-four or thirty-six, then again becoming
relaxed and flaccid. This rigid contracted state of the heart, in which
the walls are thickened and the cavities diminished, was formerly
supposed to be a result of disease, and was termed concentric hyper-
trophy; but it is now known to be the natural condition of the organ,
at the period when the rigor mortis occurs in it. — The contraction of
the arterial tubes is so great, as to produce for the time a great dimi-
nution in their calibre ; and this, doubtless, contributes to the passage
of the blood from the arterial into the venous system, which almost
invariably takes place within a few hours after death. The arteries
then enlarge again, and become quite flaccid, their tubes being emptied
of the previous contents ; and it was from this circumstance, that the
ancient physiologists were led to imagine that the arteries are not
destined to carry blood, but air.

369. As soon as the Rigor Mortis departs, the muscles pass into
a state of decomposition ; in fact, it is by the commencement of de-
composition, that the cessation of this vital property is occasioned.
Thus we may regard the Rigor Mortis as the last act of the Muscu-
lar Contractility ; and in this respect it corresponds with the coagula-
tion of the blood, which also is the closing act of its life, when it is
drawn from the living body, or has ceased to circulate (§ 184).

FORCE DEVELOPED IN MUSCULAR CONTRACTION. 221

There are, indeed, many remarkable points of correspondence be-
tween the two phenomena; which have induced some physiologists
to believe, that rigor mortis is in fact nothing else than the coagula-
tion of the blood in the muscles. It has been shown by Mr. Bowman,
however, that the stiffening of the muscles after death is due to the
permanent contraction of their component fibres, and that the coagu-
lation of the blood can have nothing to do with it. Nevertheless,
this contraction may be considered as being, for the muscular fibre,
very much the same kind of phenomenon as the coagulation of the
fluid fibrin of the blood, — especially resembling the subsequent con-
traction of the clot, which takes place gradually, within a few hours
after its separation. The causes which prevent the coagulation of
the blood after death (§ 187), usually prevent also this last manifes-
tation of the tenacity of the muscles ; their vitality being completely
destroyed, like that of the blood, by sudden and powerful shocks
operating on the nervous system, or by the complete exhaustion con-
sequent upon violent and long-continued exertion, as when animals
are run to death. And again, the tonicity of muscles survives the
freezing process ; manifesting itself by contraction and rigidity, in a
muscle that has been frozen immediately after death, and is subse-
quently thawed ; just as the peculiar properties of the fibrin of the
blood cause its coagulation upon being thawed, if it have been frozen
immediately upon being drawn from the vessels.

370. The power by which the elements of Muscular fibre are
caused to approach one another in the exercise of their Contractility,
differs from any other with which we are acquainted. Its complete
dependence upon the life of the tissue is remarkably shown by the
fact (ascertained by Valentin), that, after the cessation of the irritabi-
lity, the muscles tear with a far less weight, than they were previously
able to draw, when excited by galvanism ; so that their contractile
force is much greater than that, which the simple cohesiveness of the
tissue can sustain. Moreover, it has been shown by the experiments
of Schwann, that the contractile force is greatest, when the muscle is
most extended ; so that, with the same stimulus, it can overcome a
greater resistance by its contraction, when it has been previously
stretched to its full length, than it can when it has been already in
part shortened by the exercise of its contractile force. The power
diminishes progressively with the further shortening of the muscle ;
until at last no further contraction can be produced by any stimulus,
the extreme limit having been reached. Hence it seems as if the
contractile force of Muscles differs completely from other forms of
Attraction, as those of Gravitation, Electricity, &c.; since it is the
universal law of their operation, that the force increases, in proportion
to the decrease between the squares of the distances between the
attracting bodies ; whilst, in the case of muscle the force decreases, in
proportion as the distance between the attracting particles decreases.
But it is to be remembered that the law of attraction just quoted sup-
poses the particles to be quite free to approach one another ; and this

222 NERVOUS SYSTEM;— ITS GENERAL STRUCTURE.

they obviously are not in the contraction of a Muscle, since the ap-
proach cannot take place without a change of place between the solid
and fluid elements (§ 354). Hence it is difficult, if not impossible,
to discover the law, which shall truly express the nature of the at-
traction between the ultimate particles of Muscle at different dis-
tances ; but the law discovered by Schwann expresses the force
actually developed, at the different states of muscular contraction.

371. It has been ascertained by the researches of MM. Becquerel
and Breschet, that the temperature of a muscle rises, when it is thrown
into energetic contraction. The increase is ordinarily but about 1°
Fahr.; but it may amount to twice as much, if the muscle be kept in
action for some time, as in the exercise of sawing. Two causes may
be assigned for this increase. It may depend upon the chemical
changes which take place in the Muscles, as a necessary condition of
the production of its force (§ 361); or it maybe the result of the fric-
tion taking place between different parts, during the constant inter-
change of their actions (§ 356). Perhaps both these causes concur
in producing the effect.

372. The JYervous System, taken as a whole, is the instrument of
all those operations, which peculiarly distinguish the Animal from the
Plant; and it serves many additional purposes, connected with the
Organic or Vegetative functions, which the peculiar arrangements of
the Animal body involve. Wherever a distinct Nervous System can
be made out (which has not yet been found possible in the lowest
Animals), it consists of two very different forms of structure ; the
presence of both of which, therefore, is essential to our idea of it as
a whole. We observe, in the first place, that it is formed of trunks,
which are distributed to the different parts of the body, especially to
the muscles and to the sensory surfaces ; and of ganglia, which some-
times appear merely as knots or enlargements on these trunks, but
which, in other cases, have rather the character of central masses,
from which the trunks proceed. Now it is easily established by experi-
ment, that the active powers of the nervous system reside in the ganglia;
and that the trunks serve merely as conductors of the influence which
is to be propagated towards or from them. For if a trunk be divided
in any part of its course, all the parts to which the portion thus cut
off from the ganglion is distributed, are completely paralyzed ; that is,
no impression made upon them is felt as a sensation, and no motion
can be excited in them by any act of the mind. Or if the substance
of the ganglion be destroyed, all the parts, which are exclusively
supplied by nervous trunks proceeding from it, are in like manner
paralyzed. But if, when a trunk is divided, the portion still con-
nected with the ganglion be pinched, or otherwise irritated, sensations
are felt, which are referred to the points supplied by the separated
portion of the trunk ; which shows that the part remaining in con-
nection with the ganglion is still capable of conveying impressions,
and that the ganglion itself receives these impressions and makes
them felt as sensations. On the other hand, if the separated portion

STRUCTURE OF NERVOUS FIBRES. 223

of the trunk be irritated, motions are excited in the muscles which it
supplies ; showing that it is still capable of conveying the motor
influence, though cut off from the usual source of that influence.

373. When we minutely examine the trunks of the nerves, we find
that they are composed, in the first place, of a JYeurilemma or nerve-
sheath, consisting of white fibrous tissue ; the office of which is evi-
dently that of protecting the nerve-tubes, and of isolating them from
the surrounding structures, at the same time that it allows blood-
vessels to pass into the interior of the trunk. From the interior of
the neurilemma, thin layers of areolar tissue pass into the midst of
the enclosed bundle of nervous fibres ; separating it into numerous
smaller fasciculi, which are thus bound together, and supplied with
blood-vessels. The capillaries are distributed very much on the same
plan as those of Muscular tissue (Fig. 62); the network being com-
posed of straight vessels, which run along the course of the nerve,
between the nerve-tubes, and which are connected at intervals by
transverse vessels. — When the neurilemma has been removed, and
the trunk has been separated into its component fasciculi, we may still
further subdivide the fasciculi themselves, by careful dissection, until
we arrive at the ultimate nervous fibre, which is the essential element
of the structure. Two forms of this fibre exist in the nerves of higher
animals, bearing a considerable analogy to the two forms of the Mus-
cular fibre ; one appearing to be the special instrument of the animal
functions ; and the other, which seems to be less perfectly formed,
having a connection (the nature of which is not yet well understood)
with the organic. These require a separate description.

374. The Nervous fibre, in its most complete form, is distinctly
tubular. It is composed externally of a very delicate transparent mem-
brane, which is apparently quite homogeneous ; this is obviously
analogous to the myolemma of the Muscular fibre, and serves, like it,
to isolate the contained substance most completely from surrounding
structures. This membranous tube is not penetrated by blood-vessels,
nor does it branch or anastomose with others ; and there is reason to
believe it to be continuous from the origin to the termination of the
nervous trunk. Within the tube is a hollow cylinder of a material,
known as the White substance of Schwann, which differs in composi-
tion and refracting power from the matter that occupies the centre of
the tube, and of which the outer and inner boundaries are marked
out by two distinct lines. And the centre or axis of the tube is occu-
pied by a transparent substance, which is termed the axis-cylinder.
There is reason to believe that this last is the essential component of
the nervous fibre ; and that the hollow cylinder which surrounds it,
serves, like the external investment, chiefly for its complete isolation.
The whole of the matter contained in the tubular sheath is extremely
soft ; yielding to very slight pressure. The tubular sheath itself varies
in density in different parts ; being stronger in the nervous trunks,
than in the substance of the brain and spinal cord. In the former, it
is not difficult to show, that the regular form of the nerve-tube is a

224 STRUCTURE OF NERVOUS FIBRES AND TRUNKS.

perfect cylinder ; though a little disturbance will cause an alteration
in this, — a small excess of pressure in one part forcing the contents
of the tube towards another, where they are more free to distend it,
and thus producing a swelling. The greater delicacy of the tubular
sheath in the latter causes this result to take place with yet more
readiness ; so that a very little manipulation, exercised upon the fibres
of the brain and spinal cord, or on those of special sense, occasions
them to assume a varicose or beaded appearance, which, when first
observed by Ehrenberg, was thought to be characteristic of them.
When the fibres of these parts, however, are examined without any
such preparation, they are found to be as cylindrical as the others. —
The diameter of the tubuli is usually between l-2000th and l-4000th
of an inch. Sometimes, however, it is as much as 1-1 500th ; and
occasionally as little as l-14000th. They are larger in the nerve-
trunks than in the brain ; and they diminish in the latter as they ap-
proach the cortical substance. The fibres of the nerves of special
sense are smaller than the average, in every part of their course.

375. The organic nervous fibres (termed gelatinous by Henle) are
chiefly found in the Sympathetic system, and may be regarded as its
distinctive element; but, as we shall see hereafter (Chap. XII.), they
are mixed up with the preceding in the ordinary nervous trunks.
These fibres cannot be shown to consist of the same variety of parts
as the preceding ; no tubular envelop can be distinguished ; and the
white substance of Schwann seems wanting. They are flattened, soft,
and homogeneous in their appearance, bearing a considerable resem-
blance to the unstriped Muscular fibres ; and, like them, they contain
numerous cell-nuclei, which are arranged with tolerable regularity.
These nuclei are brought into view by acetic acid, which dissolves
the rest of the fibre, leaving them unchanged. The organic fibres are
usually of smaller size than the tubular, their diameter averaging
between the l-6000th and the l-4000th of an inch ; and they some-
times show a disposition to split into very delicate fibrillse. Being of
a yellowish- gray colour, they have been sometimes distinguished as
the gray fibres.

376. Both classes of fibres appear to run continuously, from one
extremity of the nervous cord to the other, without anything like
union or anastomosis ; each ultimate fibre probably having its distinct
office, which it cannot share with another. The fasciculi, or bundles
of fibres, however, occasionally intermix and exchange fibres with
each other ; and this interchange may take place among either the
fasciculi of the same trunk, or among those of different trunks. Its
object is evidently to diffuse among the different branches the endow-
ments of a particular set of fibres. Thus we shall hereafter see that,
in all the Spinal Nerves of Vertebrata, one set of roots ministers to
sensation, and another to motion ; the sensory fibres are principally
distributed to the skin, and the motor fibres to the muscles ; but every
branch contains both sensory and motor fibres, which are brought
together by the interlacement of those connected with both sets of

COMMUNICATIONS BETWEEN NERVOUS TRUNKS. 225

roots. In the head, we have some nervous trunks which have sen-
sory roots alone ; and others which have motor roots only ; these in
like manner acquire each other's functions in some degree by an
interchange of filaments, — the sensory trunk receiving motor fibres,
and the motor trunk receiving sensory fibres. An interchange of
this kind, upon a very extensive scale, takes place between the
Cerebro-spinal system, whose ganglionic centres are the brain and
spinal cord, and the sympathetic system, whose centres consist of a
number of scattered ganglia. The former sends a large number of
tubular fibres into the latter, by the twigs of communication near the
origins of the Spinal nerves, as well as by their connecting branches;
whilst the latter sends a smaller number oi gray or organic fibres into
the former.

377. Sometimes we find the fasciculi of several distinct trunks
united into an extensive plexus ; the sole object of which appears to
be, to give a more advantageous distribution to fibres, which all
possess corresponding endowments. Thus the brachial plexus mixes
together the fibres arising by five pairs of roots, on either side, from
the spinal cord; and sends oflf five principal trunks to supply the arm.
Now if each of these trunks had arisen by itself, from a distinct seg-
ment of the spinal cord, so that the parts on which it is distributed
had only a single connection with the nervous centres, they would
have been much more liable to paralysis than they are. By means
of the plexus, every part is supplied with fibres arising from each of
the five segments of the spinal cord ; and the functions of the whole
must, therefore, be suspended, before complete paralysis of any part
could occur, from a cause which operates above the plexus. This
may be experimentally shown on the Frog, whose crural plexus is
formed by the interlacement of the component fasciculi of three trunks
on each side; for section of the roots of one of these produces little
effect on the general movements of the limb; and even when two are
divided, there is no paralysis of any of its actions, all being weakened
in nearly an equal degree. It is possible that by the plexiform
arrangement, a consentaneousness of action is in some degree favoured,
where several distinct motions are to be combined in one movement;
something of the same kind is to be met with in numerous instances,
among the lower animals, in which the same purpose has to be
attained.

378. The second primary element of the Nervous System, without
which the fibrous portion would seem to be totally inoperative, is
composed of nucleated cells, containing a finely granular substance,
and lying somewhat loosely in the midst of a minute plexus of blood-
vessels. Their normal form may be regarded as globular (hence
they have been termed nerve or ganglion- globules) ; but this is liable
to alteration from the compression they suflTer, so that they may be-
come oval or polygonal. The most remarkable change of form,
however, which they undergo, is by an extension into one or more
long processes, giving them a caudate or a stellate aspect. These

15

VESICULAR NERVOUS SUBSTANCE.

Fig. 64.

processes, according to Messrs. Todd and Bowman, are composed
of a finely-granular substance, resembling that of the interior of the

vesicle, with which they seem to be dis-
tinctly continuous. They are very liable
to break off near the vesicle ; but if traced
to a distance, they are found to divide
and subdivide, and at last to give off some
extremely fine transparent fibres, which
seem to interlace with those of other
stellate cells, and which may perhaps
(though this is at present only a surmise)
become continuous with the axis-cylin-
ders of the nerve-tubes. The size of the
vesicles is liable to great variation; the globular ones are usually
between l-300th and 1- 1250th of an inch in diameter. — Besides the
finely-granular substance just mentioned, these cells usually contain

Capillary Network of Nervous
Centres.

Primitive fibres and ganglionic globules of human brain, after Purkinje. a, ganglionic globules
lying amongst varicose nerve-tubes, and blood-vessels, in substance of optic thalamus; a, globule
more enlarged; &, small vascular trunk, b, b, globules with variously-formed peduncles, from dark
portion of crus cerebri. 350 Diam.

a collection of pigment-granules, which give them a reddish or yel-
lowish-brown colour. This, however, is frequently absent, especially
among the lower animals.

379. The vesicles just described are aggregated together in masses
of variable size ; and are in some degree held together by the plexus
of blood-vessels, in the midst of which they lie. They are sometimes
imbedded in a soft granular substance, which adheres closely to their
exterior and to their processes; this is the case in the outer part of
the cortical substance of the human brain. In other instances, each
cell is enclosed in a distinct envelop, composed of smaller cells,
closely adherent to each other and to the contained cell ; such an

STRUCTURE OF NERVOUS GANGLIA.

227

arrangement is common in the smaller ganglia, and in the inner por-
tion of the cortical substance of the brain. — The substance, which is
made up of these peculiar cells, of the plexus of the blood-vessels
in which they lie, and of the granular matter that is disposed amongst
them, is altogether commonly known as the cineritious or gray sub-
stance ; being distinguished by its colour, in Man and the higher ani-
mals at least, from the white substance (composed of nerve-tubes) of
which the trunks of the nerves, as well as a large part of the brain
and spinal cord, are made up. But this distinction is by no means
constant; for the gray colour, which is partly due to the pigment-
granules of the cells, and partly to the redness of the blood in the
vessels, is wanting in the Invertebrata generally, and is not charac-
teristically seen in the classes of Fishes and Reptiles. Moreover,
when the ganglionic substance exists in small amount, even in Man,
its colour is not sufficiently intense to serve to distinguish it; and, as
we have already seen, there are nerve fibres which possess a grayish
hue. The real distinction evidently lies in theybrm of the ultimate
structure, which is fibrous in the one case, and cellular or vesicular
in the other ; and these terras will be henceforth used to characterize
the two kinds of Nervous tissue, which have been now described.

380. A ganglion, then, essentially consists of a collection of nerve-
vesicles or ganglion-globules, interspersed among the nerve-fibres;
and it is in the presence of the former, that it differs from a plexus,
which it frequently resembles in the arrangement of the latter. When
a nerve enters a ganglion, its component fibres separate and pass
through the ganglion in different directions, so as to be variously
distributed among the branches which pass out of it. In their

Fig. 66.

Dorsal gnnglion of Sympathelic nerve of Mouse ;— a, b, cords of connection with adjacent sympa-
thetic ganglia ; c, c. c, c, branches to the viscera and spinal nerve; rf, ganglionic globules or cells; e,
nervous fibres crossing the ganglion.

course, they come in contact with the vesicular matter, which occu-
pies the interior of the ganglion : and it appears from Mr. Newport's

228 CONNECTION OF FIBROUS AND VESICULAR STRUCTURES.

observations, that they then become softer, and that their diameter
increases. — The only exception to the general fact, that the vesicular
matter occupies the centre of the ganglia, occurs in the brain of
Vertebrata, in which it is chiefly disposed on the exterior, forming the
cortical envelop. The reason for this variation is probably to be found
in the very large amount of this substance, which the brain of the
higher Vertebrata contains ; and in the necessity of the free access
of blood-vessels to it, which is provided for by a great extension
of its surface beneath the investing vascular membrane (pia mater),
more readily than it could be in any other mode.

381. But the vesicular matter is not found in the central masses
only of the Nervous System ; for it presents itself also at those parts
of the surface or periphery^ which are peculiarly destined to receive
the impressions that are to be conveyed to the central organs. Thus
on the expansion of the optic nerve which forms the retina, there is
a distinct layer of ganglionic corpuscles or nerve-cells, with a minute
plexus of vessels ; possessing all the essential characters of the vesi-
cular substance of the brain. Something of the same kind has been
seen in connection with the corresponding expansions of the olfactive
and auditory nerves ; and it is probable that the same elements exist
in the papillce of the tongue and skin, to which the nerves of taste
and touch are distributed. In these papillae, the nervous fibres seem
to form loops, which are accompanied by similar loops of blood-ves-
sels (Figs. 67 and 68). Hence we may state it as a general fact,

Fig. 68.

Distribution of the tactile nerves at the surface of
the lip; as seen in a thin perpendicular section of
the skin.

Capillary network at margin of lips.

that, wherever a change is to be originated^ we find vesicular matter
with capillary blood-vessels ; whilst for the conduction of such a
change to distant parts, \he fibrous structure is alone required.

382. The connection between the fibrous and vesicular portions
of the Nervous system, has not yet been clearly traced. It is quite
certain that, as already remarked, many of the nerve fibres which
enter a ganglion, come into contact with its cells, passing over or
amongst them, and then issuing from it again. And this seems to be
the case also with many of the fibres which enter the vesicular matter

1^

M

CHEMICAL COMPOSITION OF NERVOUS SUBSTANCE. 229

of the Spinal cord, and the cortical substance of the brain. Some
observations recently made by Dr. Lonsdale on the structure of the
nervous system of foetuses, in which the brain and spinal cord were
wanting, present a remarkable confirmation of this view. The
nervous cords were for the most part developed ; and at their origins
(so called), or central extremities, they were found to hang as loose
threads in the cavities of the cranium and spine. On examining
these threads, it was found that the nerve-tubes of which they con-
sisted formed distinct loops, each of which was composed of a fibre
that entered the cavity and then returned from it. These loops were
imbedded in granular matter, resembling that interposed between the
vesicles in the cortical substance of the brain, and perhaps to be
regarded as vesicular substance in an early stage of its formation.
All that is known of the laws regulating the formation of irregular
productions like these, leads us to the belief, that we may rightly
consider this arrangement of the nerve-tubes as one which exists in
the nervous centres when they are fully developed. On the other
hand, the appearances observed by Messrs. Todd and Bowman appear
to indicate, that some of the fibres originate directly in the subdivisions
of the filamentous prolongations of the nerve-cells ; this, however,
must still be regarded as an unsettled question.

383. We have now to speak briefly of the Chemical Composition
of the Nervous matter; — a consideration which will be presently
shown to be of much importance. As formerly remarked (§ 7), the
vital activity of a tissue is usually greater, as the proportion of its
solid to its fluid contents is less ; and this rule holds good most strik-
ingly in regard to the Nervous substance, the vital activity of which
is far greater than that of any other tissue, and the solid matter of
which usually constitutes no more than a fourth, and occasionally
does not exceed an eighth, of its entire weight. The proportion of
water is greatest in infancy and least in middle life ; and it has been
observed to be under the average in idiots. Of the solid matter of
the brain, about a third consists of fibrin or albumen; which is pro-
bably the material of the membrane of the tubuli, as well as of the
tissue that connects them. — It is chiefly with the Fatty matter, which
constitutes about a third of the solid substance, that the attention of
Chemists has been occupied. This is stated by M. Fremy (one of
the most recent analysts) to contain, besides the ordinary fatty mat-
ters, and Cholesterine or biliary fat, two peculiar fatty acids, termed
the Cerebric and the Oleo-phosphoric. Cerebric acid, when purified, is
white, and presents itself in crystaline grains. It contains a small
proportion of Phosphorus; and diflfers from the ordinary fatty matter
in containing Nitrogen, as also in containing twice their proportion
of oxygen. Oleo-phosphoric acid is separated from the former by its
solubility in ether; it is of a viscid consistence; but when boiled for
a long time in water or alcohol, it gradually loses its viscidity, and
resolves itself into a pure oil, which is elaine, while phosphoric acid
remains in the liquor. The proportion of phosphorus in the brain is

230 WASTE AND RENEWAL OF NERVOUS SUBSTANCE.

considerable ; being from 8 to 18 parts in 1000 of the whole mass, or
from l-20th to l-30th of the whole solid matter. It seems to be un-
usually deficient in the brain of idiots. — The remaining third and
sometimes more, is composed of a substance termed Osmazome
(w^hich seems to be a proteine-compound in a state of decomposi-
tion), together with saline matter. — No satisfactory examination has
yet been made into the comparative composition of the vesicular and
fibrous substances ; but according to Lassaigne, the former contains
much more water than the latter, and little colourless fat, but nearly
4 per cent, of red fat, which does not exist in the other.

384. Various circumstances lead to the belief, that the Nervous
tissue, during the whole period of active life, is continually undergoing
changes in its substance, by decay and renewal. We know that,
after death, it is one of the first of all the animal tissues to exhibit
signs of decomposition ; and there is no reason to suppose, that this
tendency is absent during life. Hence for the simple maintenance of
its normal character, a considerable amount of nutritive change must
be required. But many circumstances further lead to the conclusion,
that, like all other tissues actively concerned in the vital operations,
Nervous matter is subject to a waste or disintegration^ which bears
an exact proportion to the activity of its operations ; — or, in other
words, that every act of the Nervous system involves the death and
decay of a certain amount of Nervous matter, the replacement of
which will be requisite in order to maintain the system in a state fit
for action. We shall hereafter see, that there are certain parts of the
Nervous system, particularly those which put in action the respiratory
muscles, which are in a state of unceasing, though moderate, activity;
and in these, the constant nutrition is sufficient to repair the effects of
the constant decay. But those parts, which operate in a more power-
ful and energetic manner, and which therefore waste more rapidly
when in action, need a season of rest for their reparation. Thus a
sense of fatigue is experienced, when the mind has been long acting
through its instrument — the brain ; indicating the necessity for rest
and reparation. And when sleep^ or cessation of the cerebral func-
tions, comes on, the process of nutrition takes place with unchecked
energy, counterbalances the results of the previous waste, and pre-
pares the organ for a renewal of its activity. In the healthy state of
the body, when the exertion of the nervous system by day does not
exceed that, which the repose of the night may compensate, it is
maintained in a condition which fits it for constant moderate exercise;
but unusual demands upon its powers, — whether by the long-con-
tinued and severe exercise of the intellect, by excitement of the emo-
tions, or by the combination of both in that state of anxiety which the
circumstances of man's condition too frequently induce, — produce an
unusual waste, which requires, for the complete restoration of its
powers, a prolonged repose.

385. There can be no doubt that (from causes which are not
known) the amount of sleep required by different persons, for the

WASTE AND RENEWAL OF NERVOUS SUBSTANCE. 231

maintenance of a healthy condition of the nervous system, varies
considerably ; some being able to dispense with it, to a degree which
would be exceedingly injurious to others of no greater mental ac-
tivity. Where a prolonged exertion of the mind has been made, and
the natural tendency to sleep has been habitually resisted, by a strong
effort of the will, injurious results are sure to follow. The bodily
health breaks down, and too frequently the mind itself is permanently
enfeebled. It is obvious that the nutrition of the Nervous system
becomes completely deranged ; and that the tissue is no longer
formed, in the manner requisite for the discharge of its healthy func-
tions.

386. As the amount of Muscular tissue that has undergone disin-
tegration, is represented (other things being equal) by the quantity of
urea in the urine, so do we find that an unusual waste of the nervous
matter is indicated by an increase in the amount of phosphatic depo-
sits. No others of the soft tissues contain any large proportion of
phosphorus ; and the marked increase in these deposits, which has
been continually observed to accompany long-continued wear o{ mind,
whether by intellectual exertion, or by anxiety, can scarcely be set
down to any other cause. The most satisfactory proof is to be found
in cases, in which there is a periodical demand upon the mental
powers ; as, for example, among clergymen, in the preparation for,
and discharge of, their Sunday duties. This is found to be almost
invariably followed by the appearance of a large quantity of the phos-
phates in the urine. And in cases in which constant and severe
intellectual exertion has impaired the nutrition of the brain, and has
consequently weakened the mental power, it is found that any pre-
mature attempt to renew the activity of its exercise, causes the
re-appearance of the excessive phosphatic discharge, which indicates
an undue waste of nervous matter.

387. As the disintegration of the Nervous System is thus propor-
tional to its exercise, so must its reparation make a corresponding
demand upon the nutritive processes. And accordingly we find, that
it is very copiously supplied with blood-vessels ; and that the amount
of food appropriated to its maintenance in an active condition, is very
considerable. This we know from the fact, that persons of active
minds, but sedentary bodily habits, commonly require nearly as much
food as those in whom the waste of the Muscular system is greater,
and that of the Nervous system less, in virtue of their bodily activity
and the less energetic operation of their minds.

388. The first development of the nerve-fibres appears to take
place, like that of Muscular fibre, by the coalescence of a number of
primary cells into a continuous tube ; the granular fatty matter within
being the product of a subsequent secreting-action. The nuclei of
the original cells may be frequently seen in the nerve-tubes at a later
period, lying between their membranous walls and the substance
deposited in their interior. It is probable that the nerve-tubes
undergo little change, from the period of their first production to

232 REGENERATION OF NERVOUS SUBSTANCE.

that of their final decay; their function, as will be presently shown,
being of a much more passive character, than that of the vesicular
substance. On the other hand, the vesicular matter appears to be in
a state of continual change, as is the case with all cells whose func-
tions are active. The appearances observed by Henle in the cortical
substance of the brain lead to the belief, that there is as continual a
succession of nerve-cells as there is of epidermic cells; their de-
velopment commencing at the surface, where they are most copiously
supplied with blood-vessels from the investing membrane, and pro-
ceeding as they are carried towards the inner layers, where they
come into more immediate relation with the fibrous portion of the
nerve-structure. This change of place is probably due to the con-
tinual death and decay of the mature cells, where they are connected
with the fibres ; and the constant production of new generations at
the external surface, — thus carrying the previously-formed cells in-
wards, in precisely the same manner that the epidermic cells are
progressively carried outwards.

389. The regeneration of Nervous tissue that has been destroyed,
takes place very readily in continuity with that which is left sound.
This may be more easily proved by the return of the sensory and
motor endowments of the part, whose nerves have been separated,
than by microscopic examination of the reunited trunks themselves,
which is not always satisfactory. All our knowledge of the functions
of the nervous system leads to the belief, that perfect continuity of
the nerve-tubes is requisite for the conduction of an impression of
any kind, — whether this be destined to produce motion or sensation ;
and various facts, well known to Surgeons, prove that such restora-
tion may be complete. In the various operations which are prac-
tised for the restoration of lost parts, a portion of tissue removed
from one spot is grafted, as it were, upon another ; its original at-
tachments are more or less completely severed, — frequently entirely
destroyed, — and new ones are formed. Now in such a part, as long
as its original connections exist, and the new ones are not completely
formed, the sensation is referred to the spot from which it was taken;
thus when a new nose is made, by partly detaching and bringing
down a piece of skin from the forehead, the patient at first feels,
when anything touches the tip of his nose, as the contact were really
with his forehead. After time has been given, however, for the
establishment of new connections with the parts, into whose neigh-
bourhood it has been brought, the old connections of the grafted
portion are completely severed ; and an interval then ensues, during
which it frequently loses all sensibility ; but after a time its power of
feeling is restored, and the sensations received through it are referred
to the right spot. — A more familiar case is the regeneration of Skin,
containing sensory nerves, which takes place in the well-managed
healing of wounds involving loss of substance. Here there must
obviously be, not merely a prolongation of the nerve-tubes from the
subjacent and surrounding trunks, but also a formation of new sen-

FUNCTIONAL CONNECTION OF BRAIN AND NERVES. 233

sory papillae. — A still more striking example of the regeneration of
Nervous tissue, however, is to be found in those cases (of which
there are now several on record), in which portions of the extremi-
ties, that have been completely severed by accident, have been made
to adhere to the stump, and have in time completely recovered their
connection with the Nervous as with the other systems, — as indi-
cated by the restoration of their sensory and motor endowments. —
Of the degree in which the vesicular substance of the Nervous sys-
tem may be regenerated, we have no certain knowledge; but there
can be little doubt, from the activity of its usual nutritive changes,
that a complete reproduction may be effected in cases of loss of sub-
stance, where it can commence from a neighbouring mass of the same
tissue.

390. We have now to inquire into the conditions under which the
peculiar properties of the Nervous System are manifested in an active
form; and it will first be desirable to explain, somewhat more in
detail, the nature of the different operations to which it is sub-
servient. These operations present themselves, in their most com-
plex form, in Man and the higher animals; but they may often be
most satisfactorily studied in the lower. In the first place, when an
impression is made upon any part of the surface of the body by
mechanical contact, by heat, electricity, or any other similar agent,
— or upon the organs of special sense (the eye and ear, the nose and
tongue), by light or sound, by odorous or sapid bodies, — these im-
pressions, in the healthy and wakeful state of the Nervous system
are felt as sensations; that is, the mind is rendered conscious of
them. Now there can be no doubt that the mind is immediately
influenced, not by the impression in the remote organ, but by a cer-
tain change in the condition of the brain, excited or aroused by that
which has originated elsewhere. For if the communication with the
brain be cut off', no impression on the distant parts of the nervous
system is felt, notwithstanding that the mind remains perfectly capa-
ble of receiving it. The mind, then, is only rendered conscious of
external objects by the influence which they exert upon the brain, or
upon a certain part of it, which, being the peculiar seat of sensation,
is called the sensorium. Hence we recognize, in the process by
which the mind is rendered conscious of external objects, three dis-
tinct stages ; — first, the reception of the impression at the extremities
of the sensory nerve ; second, the conduction of the impression,
along the trunk of the nerve, to the sensorium ; third, the change
excited by it in the sensorium itself, through which sensation is
produced. Here, then, the change in the condition of the nervous
system commences at the circumference, and is transmitted to the
centre ; and the fibres which are concerned in this transmission are
termed sensory.

391. On the other hand, when an emotion, an instinctive impulse,
or an act of the will, operates through the brain to produce a muscular
contraction, the first change is in the condition of the brain itself or of

234 ACTION OF NERVES INDEPENDENTLY OF THE BRAIN.

a certain part of it. The influence of this change is transmitted by
the motor nerves to the muscles, among which they are distributed ;
and the desired movement is the result. Here, too, we have three
stages ; first, the origination of the change by the act of the mind upon
the brain ; second, the conduction of that change along the motor
nerves ; and third, the stimulation of the muscles to contraction. But
the operation here commences at the centre ; and the effects of the
change in the brain are transmitted to the circumference, by a set of
nervous fibres which are termed motor. The complete distinctness
of these two classes of fibres was first established by Sir C. Bell. It
is best seen in the nerves of the head, of which some are purely sen-
sory, and others purely motor ; but it may also be clearly proved to
exist at the roots of the spinal nerves (although their trunks possess
mixed endowments), the posterior being sensory, whilst the anterior
are motor.

392. But although sensations can only be felt through the brain,
and voluntary motions can only be produced by an action of the mind
through the same organ, yet there are many changes in the animal
body, in which the nervous system is concerned, which yet do not
involve the operation of the brain, being produced without our con-
sciousness being necessarily excited, and without any act of the will,
or even in opposition to its efforts. Of these actions, the spinal cord
of Vertebrata, and its prolongation within the cranium, are the chief
instruments ; in the Invertebrate animals, they are performed by
various ganglia, which are usually disposed in the neighbourhood .of
the organs to which they minister. If the spinal cord of a Frog be
divided in its back, above the crural plexus, so as entirely to cut off
the nerves of the lower extremities from connection with the brain,
the animal loses all voluntary control over these limbs, and no sign of
pain is produced by any injury done to them. But they are not
thereby rendered motionless ; for various stimuli applied to the limbs
themselves will cause movements in them. Thus if the skin of the
foot be pinched, or if a flame be applied to it, the leg will be violently
retracted. Or, if the cloaca be irritated by a probe, the feet will
endeavour to push away the instrument. We have no reason hence
to believe, that the animal feels the irritation, or intends to execute
these movements, in order to escape from it ; for motions of a similar
kind are exhibited by men, who have suffered injury of the lower
part of the spinal cord, and who are utterly unconscious, either of the
irritation, or of the action their limbs perform.

393. We are not to suppose, however, that the stimulus acts at
once upon the muscles, without the nervous system being concerned
at all ; throwing them into contraction by its direct influence. For it
is quite certain that, unless the nervous trunks remain continuous
with the spinal cord, and unless the part of the spinal cord with which
they are connected remains sound (although cut off from connection
with the parts above, and with the brain), no action will be the result.
If the trunks be divided, or eitlwr of the roots by which they are con-

REFLEX ACTION.— DISTINCT NERVOUS FIBRES. 235

nected with the spinal cord be severed, or the lower portion of the
spinal cord itself be injured, no stimulation will cause the muscular
movements just described. A very good example of the necessity of
the completeness of the nervous trunks, which convey impressions to
and from the central organ, is found in the movements of the iris, for
the contraction and dilatation of the pupil. Here, the stimulus of
light upon the retina gives rise to a change in the condition of the
optic nerve ; which, being transmitted to a certain portion of the
encephalon with which that nerve is connected, excites there a motor
impulse ; and this impulse is conveyed through a distinct nerve (a
branch of the third pair) to the iris, occasioning contraction of the
pupil. Every one knows that this adjustment of the size of the pupil
to the amount of light, is effected without any exertion of the will on
his own part, and even without any consciousness that it is taking
place. It is performed, too, during profound sleep ; when the influ-
ence of light upon the retina excites no consciousness of its presence,
— when no sensation, therefore, is produced by it.

394. The class of actions thus performed, is termed reflex; and we
see that every such action involves the following series of changes.
In the first place, an impression is made upon the extremity of a
nerve, by some external agent; just as when sensation is to be pro-
duced. Secondly, this impression is transmitted by a nervous trunk
to the spinal cord in Vertebrata, or to some ganglionic mass which
answers to it in the Invertebrata. But instead of being communi-
cated by its means to the mind, and becoming a sensation, it imme-
diately and necessarily executes a motor impulse ; which is reflected
back as it were to certain muscles, and by their contraction, gives rise
to a movement. We shall hereafter see, that nearly all those move-
ments in the animal body, which are immediately connected with the
maintenance of the organic functions, such as those of respiration,
deglutition (or swallowing), the expulsion of the feces, urine and
fogtus, &c. — are performed in this manner.

395. Now there is no reason to believe, that the mode in which
impressions are conducted by the nervous trunks, whether towards
or from the nervous centres, is in any way different from that which
takes place, when sensations are to be produced, or voluntary motions
executed. The endowments of the trunks appear to be the same in
both instances ; but those of the centres are different. We shall here-
after see, that the very same trunks contain fibres, originating at the
same part of the surface, of which some go to the brain, and others to
the spinal cord ; impressions on the former, therefore, will produce
sensations, whilst similar impressions on the latter will give rise to no
sensations, but will excite a motor influence in immerfia^e respondence
to their call. Again, the motor fibres which pass forth from the spinal
cord, and which convey the reflex influence created by its vesicular
substance, are bound up in the same trunk with others, which proceed
from the brain, and which convey the influence of the will, communi-
cated through its gray or vesicular matter. Thus we have at least

236

NATURE OF THE NERVOUS POWER.

two sets of fibres conveying impressions inwards or centripetally ; one
of them being; sensory (as already explained § 390) in virtue of its
connection with the brain ; whilst the other is excitor^ or destined to
excite reflex movements, through the spinal cord. These, taken
collectively, may be termed afferent or centripetal fibres. On the
other hand, there are at least two sets of fibres conveying motor im-
pulses to the muscles; one of them communicating the influence of
the mind, operating through the brain ; whilst the other merely trans-
mits the reflex power of the spinal cord. These in conjunction may
be called efferent or centrifugal fibres. The following diagram may
assist the Student in comprehending the relations of the elementary
pans of the Nervous System.

396. Of the mode by which the eflfects of changes in one part of
the Nervous System, are thus instantaneously transmitted to another,
nothing whatever is known. There is evidently a strong analogy
between this phenomenon, and the instantaneous transmission of the

Diagram of the origins and terminations of the dif-
ferent groups of nervous fibres ;— a, o, vesicular sub-
stance of the spinal cord; 6, 6, 6, vesicular substance
of the brain; e, vesicular substance at the commence-
ment of afferent nerve, which consists of, cl, the ce-
rebral division, or sensory nerve, passing on to the
brain, and si, the spinal division, or excilor nerve,
which terminates in the vesicular substance of the
spinal cord; on the other side we have the efferent or
motor nerve proceeding to the muscle d, likewise con-
sistingof two divisions, — c2, the cerebral portion, pro-
ceeding from the brain, and conveying the influence
of the will or of instinct; and 52, the spinal division,
conveying the reflex power of the spinal cord.

Electric power along good conductors ; and there is this further
analogy between the Nervous and Electric agencies, that the latter
will produce many of the eflfects of the former. Thus a very feeble
galvanic current transmitted along a motor nerve, serves to excite
contractions in the muscles supplied by it ; and in like manner, a
galvanic current transmitted along any of the sensory nerves, gives
rise to a sensation of the kind to which the nerve ministers. Moreover,
we shall hereafter see, that certain animals are capable of generating
Electric power in a very remarkable manner (Chap. X.); and that the
nervous system is in some way essentially concerned in this opera-
tion. But on the other hand, it is quite certain that the influence
transmitted along the nerves of the living body is not ordinary
electricity; for all attempts to procure manifestations of electric
changes in the state of nerves, that are acting most energetically on
muscles, have completely failed ; and a nerve remains capable of
conveying the influence of electricity, when it has been rendered
unable to transmit the influence of the brain, — as by tying a ligature

CONDITIONS OF NERVOUS ACTION. 237

round it, or by tightly compressing it between the forceps, which
gives no interruption to the one agency, whilst it completely checks
the other. — Notwithstanding, then, the strong analogy which exists
between these two powers, we are not warranted in regarding them
as identical; although it is very possible that the Nervous power may
be in time showm (as Magnetism has been proved) to be a peculiar
modification of ordinary Electricity, acting under circumstances in
many respects dissimilar, and therefore appearing to possess distinct
properties.

397. It is more desirable, however, that we should understand the
conditions under which the phenomena of the Nervous system take
place, than that we should spend much time in discussing the identity of
its peculiar powers with any others in Nature. The conducting Yiowei
of the nervous fibres appears to remain with little decrease for some
time after death, especially in cold-blooded animals ; for we can, by
pinching, pricking, or otherwise stimulating the motor trunks, give
rise to contractions in the muscles supplied by them, exactly as during
life. This power is much lessened by the influence of narcotics; so
that if a nervous trunk be soaked in a solution of opium, belladonna,
or other powerful narcotic, it ceases to be able to convey the eflfects
of stimuli to the muscles, some time before the muscles themselves
lose their contractile power. On the other hand, it seems to be
exalted by various irritating influences ; so that, when the nervous
trunk has been treated with strychnia, or when it has been subjected
to undue excitement in other ways, a very slight change is magnified
(as it were) during its transmission, and produces effects of unusual
intensity.

398. Now although the conducting power of the fibrous structure
will continue for a time, after the circulation through it has ceased,
the peculiar endowments of the vesicular substance, by which it ori-
ginates the changes which the former transmits, are only manifested,
when blood is moving through its capillaries. Thus if the circula-
tion through the brain cease but for a moment, total insensibility, and
loss of the power of voluntary motion, immediately supervene. The
brain is supplied with blood through four arteries, — the two internal
carotids, and the two vertebrals ; and by the communication of these
with each other through the circle of Willis, the circulation will still
be kept up, if only one of them should convey blood into the cavity
of the cranium. Hence it is necessary that the flow of blood should
be checked through all of them, in order that the functions of the
brain should be suspended ; and the suspension is then complete and
instantaneous. The best method of effecting this was devised by Sir
Astley Cooper. He tied both the carotid arteries in a dog; which,
for the reason just mentioned, did not produce any decided influence
on the functions of the brain, the circulation being kept up through
the vertebrals. But upon compressing the latter, so as to suspend the
flow of blood through them, immediate insensibility, and loss of vo-
luntary power, were the result. When the compression was taken

238 DEPENDENCE OF NERVOUS POWER ON SUPPLY OF BLOOD.

off, the animal immediately returned to its usual state ; and again
became suddenly insensible, when the pressure was renewed. Al-
though the functions of the brain were thus suspended, those of the
spinal cord were not ; as was shown by the occurrence of convulsive
movements. But in the state called Syncope^ or fainting, the suspen-
sion of the circulation, by a failure in the heart's action, causes an
entire loss of power in both these centres ; and a complete cessation
of muscular movement is the result. This condition may come on
instantaneously, under the influence of powerful mental emotion, or
of some other cause, which act primarily in suspending the heart's
action, and consequently in checking the circulation; the insensi-
bility, and loss of muscular power, are secondary results, depending
upon the suspension of the powers of the nervous centres, consequent
upon the cessation of the flow of blood through them.

399. The due activity of the vesicular nervous matter is not only
dependent upon a sufficient supply of blood, but it requires that this
blood should be in a state of extreme purity ; for there is no tissue in
the body, whose functions are so readily deranged, by any departure
from the regular standard in the circulating fluid, — whether this con-
sist in the alteration of the proportions of its normal ingredients, or
in the introduction of other substances which have no proper place
in it. One of the most fertile sources of disturbance in the action of
the brain, consists in the retention of substances within the blood,
which ought to be excreted from it. We shall hereafter see, that
three of the largest and most important organs in the body, — the
lungs, the liver, and the kidneys, — have it for their special office, to
separate from the circulating fluid the products of the decomposition,
which is continually taking place in the body ; and thereby to main-
tain its purity, and its fitness for its important functions. Now if
these, from any cause, even partially fail in their office, speedy dis-
turbance of the functions of the nervous centres is the result. Thus
if the lungs do not purify the venous blood of its impregnation of
carbonic acid, or restore to it the proper proportion of oxygen, the
functions of the brain are seriously affected. The sensations become
indistinct, the will loses its control over the muscles, giddiness and
faintness come on, and at last complete insensibility supervenes.
Corresponding symptoms occur, though to a less serious degree,
when the excretion of carbonic acid is but slightly impeded. Thus
when a number of persons are shut up in an ill-ventilated apartment,
for a sufficient length of time to raise the proportion of carbonic acid
in the air to 1 or 2 per cent, the continued purification of their blood
by respiration is but insufficiently performed, for reasons which will
be stated hereafter (Chap. VIII.); and the carbonic acid accumulates
in their blood in a sufficient degree, to produce headache and obtuse-
ness of the mental powers. — Similar results take place, as will be
shown hereafter, from the retention of the substances, which ought to
be drawn off by the liver and kidneys; these, when they accumulate
in even a trifling degree, produce torpor of the functions of the brain;

EFFECTS OF STIMULANTS UPON NERVOUS POWER. 239

and, when their proportion increases, complete cessation of its pow-
ers is the result, their action being precisely that of narcotic poisons.
Various substances introduced into the blood may exert similar influ-
ences ; depressing the activity of the vesicular substance of the nerv-
ous centres, and consequently producing torpidity, not merely in
regard to the reception of impressions, and the performance of volun-
tary motions, but also in the mental operations generally.

400. On the other hand, various conditions of the blood, espe-
cially those depending on the presence of certain external agents,
produce an undue energy in the functions of the nervous centres;
which energy, however, is almost invariably accompanied by irregu-
larity, or want of balance among the different actions. Of this we
have a familiar example in the operation of alcohol. Its first effect,
when taken in moderate quantity, is usually to produce a simple
increase in the activity of the cerebral functions. A further dose,
however, occasions not merely an increase, but an irregularity; de-
stroying that powder of self-control, w^hich is so important a means of
balancing the different tendencies in the healthy condition of the
mind. And a still larger dose has the effect of a narcotic poison;
producing diminution or suspension of activity in all the functions of
the brain. In sonae persons, this is the mode in which the alcohol
acts from the first,-^its stimulating effects being altogether wanting.
— A similar activity is usually produced by the respiration of the
nitreous oxide; which seems to increase all the powers of the mind,
save that of self-control, which it diminishes; the individual, while
under its influence, being the slave of his impulses, which act on
his muscular system with astonishing energy. Very analogous to
this, is the incipient stage of mania, which is simply an undue
energy of the cerebral functions, at first in some degree under the
control of the will, but afterwards increasing to an extent that ren-
ders the individual completely powerless over himself; and showing
itself in the intensity of the sensations produced by external objects,
in the vividness of the trains of thought, (which, being entirely
uncontrolled, succeed each other with apparent irregularity, though
probably according to the laws of association and suggestion,) and in
the violence of the muscular actions. Such a state may continue for
some time, without the intervention of sleep; but the subsequent
exhaustion of nervous power is proportioned to the duration of the
excitement ; and frequent attacks of mania almost invariably subside
at last into imbecility.

401. In these cases of undue excitement, there is obviously an
increase in the supply of blood to the head, as indicated by the suf-
fusion of the face, the injection of the conjunctiva, the throbbing at
the temples, the pulsation of the carotids ; and we find that measures
which diminish the activity of the circulation through the brain are
those most effectual in subduing the excitement. But it does not at
all follow, that this undue action of the brain should be connected
with an excess in the whole amount of nutritive material, and should

240 DEPENDENCE OF NERVOUS POWER ON SUPPLY OF BLOOD.

require general depletion for its treatment. In fact, a very similar
class of symptoms may present itself under two conditions of an
entirely opposite kind, — inflammation^ accompanied with an increase
in the proportion of fibrin in the blood, and requiring treatment of
a lowering kind, — and irritation^ depending on a state of blood in
which there is a deficiency of solid materials, and requiring a
strengthening and even a stimulating regimen. The skill of the
practitioner is often put to the test, in the due discrimination between
these states.

402. The preceding examples mark the influence of various causes
upon the actions of the vesicular matter of the hrain; others might be
adduced to show that the vesicular substance of the spinal cord is
also liable to have its powers depressed or excited ; but these will
be best adverted to hereafter, when the distinct functions of that
organ are under consideration (Chap. XII.). We may simply notice,
that the stimulating effect of Strychnia is peculiarly and most re-
markably exerted upon the vesicular substance of the spinal cord ;
and that a corresponding state, in which violent convulsive actions
are excited by the most trifling causes, sometimes presents itself as a
peculiar form of disease, named Tetanus, which may be either idio-
pathic^ depending probably upon a disordered condition of the blood,
or traumatic^ consequent upon the irritation of a wound.

403. But, as formerly remarked, it is not in the Nervous centres
only that changes originate. Whenever an impression is made upon
the surface of the body, or upon the organs of special sense, which,
being conducted to the nervous centres, either excites a sensation in
the brain (§ 390), or a reflex action through the spinal cord (§ 392),
the reception and propagation of such impression at the extremities of
the sensory nerve requires a set of conditions of the same kind with
those which we have seen to exist in the nervous centres. In fact,
if we regard the course of the motor nerves as commencing in the
nervous centres and terminating in the muscles, we may with equal
justice consider that of the sensory nerves as originating in their
peripheral extremities, and terminating in the sensorium. And, as
already stated (§ 381), precisely the same kind of vesicular structure
exists in some (probably in all) of the peripheral expansions of the
sensory nerves as makes up the gray substance of the brain and
spinal cord. Now it is easily shown, that the circulation of blood
through these parts is just as necessary for the original reception of
the impressions, as is the circulation through the brain to their re-
ception as sensations, and to the origination of motor impulses by an
act of the will. W^e find that anything which retards the circula-
tion through a part supplied by sensory nerves, diminishes its sensi-
bility; and that if the flow of blood be completely stagnated, entire
insensibility is the result. A familiar example of this is seen in the
effects of prolonged cold, which, by diminishing, and then entirely
checking, the flow of blood through the skin, produces first numb-
ness, and then complete insensibility of the part. This result, how-

DEPENDENCE OF NERVOUS POWER ON SUPPLY OF BLOOD. 241

ever, may be partly due to the direct influence of the cold upon the
nerve-vesicles themselves, depressing their peculiar vital powers (§
97). The same effect is produced, however, when the supply of
blood is checked in any other way ; as, for example, by pressure on
the artery, or by obstruction in its interior. Thus, when the main
artery of a limb is tied, numbness of the extremities is immediately
perceived ; and this continues until the circulation is re-established
by the collateral branches, when the usual amount of sensibility is
restored. Again, in the gangrene which depends upon obstruction
of the arterial trunks by a fibrinous clot in their interior, diminution
of sensibility, consequent upon the insufficient circulation, is one of
the first symptoms.

404. On the other hand, increased circulation of blood through a
part produces exaltation of its sensibility ; that is, the ordinary im-
pressions produce changes of unusual energy in its sensory nerves.
This is particularly evident in the increased sensibility of the genital
organs of animals during the period of heat; and in those of Man,
when in a state of venereal excitement. Moderate warmth, friction,
exercise, and other causes which increase the circulation through a
part, also augment its sensibility ; and this augmentation is one of the
most constant indications of that state of determination of blood, or
active congestion, which usually precedes inflammation, and which
exists in the parts surrounding the centre of inflammatory action.
But it must be borne in mind, here as elsewhere (§ 401), that such
exaltation of function in a limited part, is quite consistent with gene-
ral debility ; and in fact we may often observe, that the tendency to
such local aflfections is particularly great, when the blood is in a very
poor condition. (See Chap. V.)

405. To sum up, then, we may compare the vesicular substance,
wherever it exists, to a galvanic combination : the former being capa-
ble of generating nervous influence, and transmitting it along the
fibrous structure, to the part on which it is to operate ; in the same
manner as the latter generates electric power, and transmits it along
the conducting wires, to the point at which it is to effect a decompo-
sition or any other change. In one of the most perfect forms of the
galvanic battery (that invented by Mr. Smee), although the metals
remain inserted in the acid solution, and are consequently always
ready for action, no electricity is generated until the circuit is com-
plete; and the waste of the zinc produced by its solution in the acid,
is therefore exactly proportional to the electric effects to which it gives
rise. The condition of the nervous system, in the healthy and waking
state, bears a close analogy to this ; for it is in a state constantly ready
for action, but waits to be excited ; and its w^aste is proportional to
the activity of its function. The vesicular matter, diffused over the
surface of the body, is inactive, until an impression is made upon it
by some external agent ; but a change then takes place in its con-
dition (of which we know no more, than that the presence of arterial

16

242 CONNECTION OF NERVOUS SYSTEM WITH MIND.

blood and a certain amount of warmth are necessary for it), which is
transmitted to the central organs by the sensory trunks. It would
appear that the excitement of this change has a tendency to increase
the afflux of blood to the part ; thus when a lozenge or some similar
substance is allowed to lie for a time in contact with the tongue, or
with the side of the mouth, a roughness is produced, which is due to
the erection of the sensory papillae, by the distension of their blood-
vessels. On the other hand, the change in the vesicular matter of
the central organs, by which motion is produced in the distant mus-
cles, may be excited either by the stimulus conveyed by the afferent
nerves (as in reflex action, § 392), or by an act of Mind. This act
may be voluntary, originating in the will ; or it may be instinctive or
emotional, resulting from certain states of mind excited by sensations,
and altogether independent of the will. Of the mode in which the
mind thus acts upon the nervous system, we know nothing whatever,
and probably never shall be informed in our present state of being.
But it is sufficient for us to be aware of the physiological fact of the
peculiar connection between the mind and the brain ; a connection so
intimate, as to enable the mind to receive through the body a know-
ledge of the condition of the Universe around it, and to impress on
the body the results of its own determinations ; and of such a nature,
that the regularity of the working of the mind itself is dependent upon
the complete organization of the brain in the first instance, upon the
constant supply of pure and well-elaborated blood, and upon all those
influences which favour the due performance of the nutritive opera-
tions in general.

BOOK II.

SPECIAL PHYSIOLOGY.

CHAPTER IV.

OF FOOD, AND THE DIGESTIVE PROCESS.

1 . Sources of the Demand for Jiliment,

406. The dependence of all Organized beings upon food or aliment,
must be evident from the facts stated in the preceding portion of this
Treatise. In the first place, the germ requires a large and constant
supply of materials, with which it may develop itself into the perfect
being, by the properties with which it is endowed. In all but the
lowest tribes of Plants, we find the materials required for the earliest
stages of the process prepared and set apart by the parent. Thus in
the seed^ the germ itself forms but a small proportion of the whole
substance, the principal mass being composed of starchy matter, which
is laid up there for its nutrition ; and the act of germination consists
in the appropriation of that nutriment by the germ, and the consequent
development of the latter, up to the point at which it becomes inde-
pendent of such assistance, and is able for itself to procure, from the
soil and atmosphere that surround it, the materials for its continued
growth. So in the egg of the Animal, the principal mass is composed
of Albumen and oily matter; the germ itself being, at the time the
egg is first deposited, a mere point invisible to the naked eye ; these
materials serve as the food or aliment of the germ, which gradually
draws them to itself, and converts them into the materials of its own
structure, and at the end of a certain period the young animal comes
forth from the egg ready to obtain for itself the food which is neces-
sary for its continued increase in size.

407. In many instances among the lower animals, the form in
which the young animal emerges from the egg is very diflferent from
that which it is subsequently to assume; and the latter is only attained
by a process of metamorphosis. This change has been longest known,
and most fully studied, in the case of Insects and Frogs; which

244 SOURCES OF THE DEMAND FOR ALIMENT.

were formerly thought to constitute an exception to all general rules
in this respect, — the Insect coming forth from the egg in the state of a
Worm, and the Frog in the condition of a Fish. But it is now known
that changes of form, as complete as these, occur in a large propor-
tion of the lower tribes of Animals; so that the absence of them is the
exception. The fact seems to be, that the supply of nutriment laid
up within the egg, among the lower classes, is by no means sufficient
to carry on the embryo to the form it is subsequently to attain ; and
its development is so arranged that it may come into the world in a
condition which adapts it to obtain its own nutriment, and thus to
acquire for itself the materials of its further development. Thusthe
Insect, in its larva or Caterpillar state, is essentially a foetus in regard
to its grade of development ; but it is a foetus capable of acquiring
its own food. In this condition it attains its full growth as regards size,
though its form remains the same ; but it then, in passing into the
Chrysalis state, reassumes (as it were) the condition of an embryo
within the egg,— the development of various new parts takes place,
at the expense of the nutriment stored up in its tissues, — and it comes
forth as the perfect insect. In many of the lower tribes, the animal
quits the egg at a still earlier period in comparison ; thus it has been
lately shown by M. Milne Edwards, that some of the long marine
worms consist only of a single segment, forming a kind of head, when
they leave the egg ; and that the other segments, to the number, it
may be, of several hundred, are gradually developed from this, by a
process that resembles the budding of Plants.

408. Up to the period, then, when the full dimensions of the body
have been attained, and the complete evolution of all its organs has
taken place, a due supply of food is necessary for these purposes. In
the Plant nearly the whole of the alimentary materials taken into the
system, are thus appropriated; the extension of its structure going on
almost indefinitely, and the waste occasioned by decay being compara-
tively small. Thus the carbon, which is given out by the respiratory
process in the form of carbonic acid, bears but a small proportion to
that, which is introduced by the decomposition of that same gas, under
the influence of light (§ 81). And the fall of the leaves, which takes
place once a year or more frequently, and which gives back a large
quantity of the matter that has undergone the organizing process, does
not occur, until by their means a considerable addition has been made
to the solid and permanent substance of the tree.

409. This is not the case, however, with the Animal. Its period
of increase is limited. The full size of the body is usually attained,
and all the organs acquire their complete evolution at a comparatively
early period. The continued supply of food is not then requisite for
the extension of the structure, but simply for its maintenance ; and the
source of the demand lies in the constant waste, to which, during its
period of activity, it is subjected. We have seen that every action of
the Nervous and Muscular systems involves the death and decay of a
certain amount of the living tissue, — as indicated by the appearance of

SOURCES OF DEMAND FOR FOOD. 245

the products of that decay in the Excretions; and a large part of the
demand for food will be consequently occasioned by the necessity for
making good the loss thus sustained. Hence we find that the demand
for food bears a close relation to the activity of the animal functions ;
so that a diet, which would be superfluous and injurious to an indi-
vidual of inert habits, is suitable and beneficial to one who is leading
a life of continual exertion; and this diflference manifests itself in the
requirements of the same individual who makes a change in his habits,
— the indolent man acquiring an appetite by vigorous exertion, and
the active man losing his disposition to hearty feeding by any cause
that keeps him from his accustomed exercise. We see precisely the
same contrast between Animals of different tribes, whose natural
instincts lead them to different modes of life. The Birds of most
active flight, and the Mammals which are required to put forth the
greatest efforts to obtain their food, need the largest and most constant
supplies of nutriment; but even the least active of these classes stand
in remarkable contrast with the inert Reptiles, whose slow and feeble
movements are attended with so little waste, that they can sustain life
for weeks and even months, with little or no diminution of their usual
activity, without a fresh supply of food.

410. The waste and decay just adverted to, however, do not affect
the muscular and nervous tissues alone ; for all the operations of
nutrition involve it to a certain extent. It has been already shown
that the acts of absorption, assimilation, respiration, secretion, and
reproduction, — all those, in fact, by which the material for the nutri-
tion of the nervous and muscular tissues is first prepared, and sub-
sequently maintained in the requisite purity, — are effected in the
Animal, as in the Plant, by the agency of cells, which are continually
dying and requiring renewal. In most Vegetables, the death of the
parts concerned in these functions takes place simultaneously, as soon
as they have performed them ; the whole crop of leaves ceasing at
once to perform its proper actions, and dropping off; — to be replaced
by another, at an interval that solely depends upon the temperature
under which the tree is living (§ 99). In the evergreen, however,
the process bears a close resemblance to that which we observe in
the Animal ; for the leaves die one by one, and not simultaneously ;
and are constantly undergoing replacement, so that the vigour of the
system and the activity of its nutritive processes never suffer a com-
plete suspension.

411. In the Animal body, the different classes of cells, to which
allusion has been made, are in like manner constantly undergoing
death and renewal; and this with a rapidity proportioned to the
energy of their functions. Hence a supply of food is as requisite to
furnish the materials of their growth, as it is in Plants to furnish the
materials of the growth of the leaves. A large part of these materials
are subsequently used for other purposes in the economy ; thus, as the
leaves prepare the sap which is to nourish the woody stem, and to
form new shoots, so do the absorbing and assimilating cells prepare

246 SOURCES OF DEMAND FOR FOOD.

and furnish the fluid elements of the blood, which are to repair the
waste of nerre and muscle, bone and cartilage, &c. But still a con-
siderable amount is expended in the simple nutrition of these organs
themselves, whose duration is transient, and whose solid parts are
cast off as of no further use. Thus the skin and all the mucous sur-
faces are continually forming and throwing off epidermic and epithelial
cells, whose formation requires a regular supply of nutriment ; and only
a part of this nutriment (that which occupies the cavity of the cells)
consists of matter, that is destined to serve some other purpose in the
system, or that has already answered it; the remainder (that of which
the solid walls are composed) being furnished by the nutritive mate-
rials of the blood, and being henceforth altogether lost to it. — Thus
every act of Nutrition involves a waste or decay of Organized tissue.
412. We may observe a marked difference, however, between the
amount of aliment required, and the amount of waste occasioned, by
the simple exercise of the nutritive or vegetative functions in the
building-up and maintenance of the animal body, and that which
results from the exercise of the animal functions. The former are
carried on, with scarcely any intermixture of the latter, during fcetal
life. The aliment, in a state of preparation, is introduced into the
foetal vessels; and is conveyed by them into the various parts of the
structure, which are developed at its expense. The amount of waste
is then very trifling, as we may judge by the small amount of excre-
tory matter, the product of the action of the liver and kidneys, w^hich
has accumulated at the time of birth ; although these organs have
attained a sufficient development to act with energy when called upon
to do so. But as soon as the movements of the body begin to take
place with activity, the waste increases greatly ; and we even observe
this immediately after birth, w-hen a large part of the time is still
passed in sleep, but when the actions of respiration involve a constant
employment of muscular power. — In the state of profound sleep^ at
subsequent periods of life, the vegetative functions are performed,
with no other exercise of the animal powers, than is requisite to sus-
tain them ; and we observe that the w^aste, and the demand for food,
are then diminished to a very low point. This is well seen in many
animals, which lead a life of great activity during the warmer parts
of the year, but which pass the winter in a state of profound sleep,
without, however, any considerable reduction of temperature ; the
demand for food, instead of being frequent, is only felt at long inter-
vals, and the excretions are much reduced in amount. And those
animals which become completely inert, either by the influence of
cold, or by the drying-up of their tissues, do not suffer from the pro-
longed deprivation of food ; because not only are their animal func-
tions suspended, but their nutritive operations also are in complete
abeyance ; and the continual decomposition of their tissues, which
would otherwise be taking place, is checked by the cold or desicca-
tion ; so that the whole series of changes which goes on in their active
condition is completely at a stand.

SOURCES OF DEMAND FOR FOOD. 247

413. But there is another most important cause of demand for food,
amongst the higher Animals, which does not exist either amongst the
lower Animals, or in the Vegetable kingdom. We have seen (Chap.
II.) that Mammals and Birds, and to a certain extent Insects also,
are able to sustain the heat of their bodies at a fixed standard, and
thus to be independent of variations in external temperature. This
they are enabled to do, as will be explained hereafter, by a process
strictly analogous to ordinary combustion ; the carbon and hydrogen
directly supplied by their food, or after having been employed for a
time in the composition of the living tissues and then set free, being
made to unite with oxygen introduced by the respiratory process, and
thus giving off the same heat as if the same materials were burned
in a furnace. And it has been further shown, that the immediate
cause of death in a warm-blooded animal, from which food has been
entirely withheld, is the inability any longer to sustain the temperature,
which is requisite for the performance of its vital operations (§ 117).
Hence we see the necessity for a constant supply of aliment, in the
case of warm-blooded animals, for this purpose alone ; and the de-
mand will be chiefly regulated by the external temperature. When
the heat is rapidly carried off from the surface, by the chilling influ-
ence of the surrounding air, a much greater amount of carbon and
hydrogen must be consumed within the body, to maintain its proper
heat, than when the air is nearly as warm as the body itself; so that
a diet which is appropriate to the former circumstances, is superfluous
and injurious in the latter; and the food which is amply sufficient in
a warm climate, is utterly destitute of power to enable it to resist the
influence of severe cold. This is a fact continually experienced ;
both in the ordinary recurrence of changes of temperature in our own
climate ; and, still more remarkably, when the same individual is
subjected to the extremes of heat and cold, in successively visiting
the tropical and frigid zones.

414. Thus we find that in the Animal body, aliment is ordinarily
required for four different purposes. First, for the original construc-
tion or building-up of the organism. Second, to supply the loss occa-
sioned by its continual decay, even when in a state of repose. Third,
to compensate for the waste occasioned by the active exercise of the
nervous and muscular systems. And Fourth, to supply the materials
for the heat-producing process, by which the temperature of the body
is kept up. — The amount required for these several purposes will
vary according to the conditions of the body, as regards exercise or
repose, and external heat or cold. It is also subject to great varia-
tion with difference of age. During the period of growth, it might
be anticipated that a larger supply of food would be required, than
when the full stature has been attained ; but a very small daily addi-
tion would suffice in the case of a child or youth, to produce the
entire increase of a whole year. Yet every one knows that the child
requires much more food than the adult, in proportion to his compa-
rative bulk. This results from the much more rapid change in the

248 SOURCES OF DEMAND FOR FOOD.

constituents of his body; which is evident from the large proportional
amount of his excretions, from the quickness with which the effects
of illness or of deficiency of food manifest themselves in the diminu-
tion of the bulk and firmness of the body, from the short duration of
life when food is altogether withheld, and from the readiness with
which losses of substance by disease or injury are repaired, when the
nutritive processes are restored to their full activity. The converse
of all this holds good in the aged person. The excretions diminish
in amount, the want of food may be sustained for a longer period,
losses of substance are but slowly repaired, and everything indicates
that the interstitial changes are performed with comparative slowness;
and, accordingly, the demand for food is far less in proportion to the
bulk of the body than it is in the adult, and may be even absolutely
less than in the child of a fourth of its weight.

415. The demand for food is increased by any cause, which creates
an unusual di'ain or waste in the system. Thus an extensive suppu-
rating action can be sustained only by a large supply of highly-nutri-
tious food. The mother, who has to furnish the daily supply of milk
w^hich constitutes the sole support of her offspring, needs an unusual
sustenance for this purpose. And there are states of the system, in
which the solid tissues seem to possess an unusual tendency to decom-
position, and in which an increased supply of aliment is therefore
required. This is the case, for example, in diabetes ; one of the first
symptoms of which disease is the craving appetite, that seems as if it
would never be satisfied. And there can be no doubt that, putting
aside all the other circumstances that have been alluded to, there is
much difference amongst individuals, in regard to the rapidity of the
changes which their organism undergoes, and the amount of food
required for its maintenance.

416. The influence of the supply of food upon the size of the indi-
vidual, is very evident in the Vegetable kingdom; and it is most
strikingly manifested, when a plant naturally growing in a poor dry
soil is transferred to a damp rich one, or when we contrast two or
more individuals of the same species, growing in localities of opposite
characters. Thus, says Mr. Ward, " I have gathered, on the chalky
borders of a wood in Kent, perfect specimens in full flower of Ery-
thrcea Centaurium (Common Centaury), not more than half an inch
in height ; consisting of one or two pairs of most minute leaves, with
one solitary flower : these were growing on the bare chalk. By trac-
ing the plant towards and in the wood, I found it gradually increasing
in size, until its full development was attained in the open parts of
the wood, where it became a glorious plant four or five feet in eleva-
tion, and covered with hundreds of flowers." On the other hand, by
starvation, naturally or artificially induced. Plants may be dwarfed,
or reduced in stature : thus the Dahlia has been diminished from six
feet to two ; the Spruce Fur from a lofty tree to a pigmy bush ; and
many of the trees of plains become more and more dwarfish as they
ascend mountains, till at length they exist as mere underwood. Part

INFLUENCE OF VARIATIONS IN SUPPLY OF FOOD. 249

of this effect, however, is doubtless to be attributed to diminished
temperature ; which, as already remarked, concurs with deficiency of
food in producing inferiority of size.

417. Variations in the supply of food would not appear to Ije
effectual in producing a corresponding variety of size in the Animal
kingdom : this is not, however, because Animals are in any degree
less dependent than Plants upon a due supply of food ; but because
such a limitation of the supply, as would dwarf a Plant to any con-
siderable extent, would be fatal to the life of an Animal. On the
other hand, an excess of food, which (under favourable circum-
stances) would produce great increase in the size of the Plant, would
have no corresponding influence on the Animal ; for its size appears
to be restrained within much narrower limits, — its period of growth
being restricted to the early part of its life, and the dimensions proper
to the species being rarely exceeded in any great degree. Even in
the case of giant individuals, it does not appear that the excess of
size is produced by an over-supply of food ; but that the larger sup-
ply of food taken in is^ called for by the unusual wants of the system,
— those wants being the result of an extraordinary activity in the pro-
cesses of growth, and being traceable rather to the properties inherent
in the system, than to any external agencies. Thus we not unfre-
quently hear of children, who have attained an extraordinary size at
the age of a few years ; and this excess of size is usually accompanied
with other marks of precocious development. We shall hereafter see,
that a provision exists in the Digestive apparatus, which absolutely
prevents the reduction and preparation of the food, in any amount
greatly surpassing that which the wants of the system demand (§ 474) ;
and it is probably to this cause, in part, that we are to attribute the
small degree of influence exerted by an excess of food, in producing
an increased development of the Animal frame.

418. The influence of a diminished supply of food, in producing a
marked inferiority in the size of Animals, is most effectually exerted
during those early periods of growth, in which the condition of the
system is most purely Vegetative. Thus it is well known to Ento-
mologists, that, whilst it is rare to find Insects departing widely from
the average size on the side of excess, dwarf-individuals, possessing
only half the usual dimensions, or even less, are not uncommon ; and
there can be little doubt that these have suffered from a diminished
supply of nutriment during their larva state. This variation is most
apt to present itself in the very large species of Beetles, which pass
several years in the larva state ; and such dwarf- specimens have even
been ranked as sub-species. Abstinence has been observed to pro-
duce the effect, upon some Caterpillars, of diminishing the number of
moults and accelerating the transformation ; in such cases, the Chry-
salis is more delicate, and the size of the perfect Insect much below
the average.

419. One of the most remarkable examples known, of the effect of
food in modifying the development of Animals, is to be found in the

250 INFLUENCE OF VARIATIONS IN SUPPLY OF FOOD.

economy of the Hive-Bee. In every community, the majority of
Individuals consists of neuters ; which may be regarded as females,
having the organs of the female sex undeveloped ; and which, whilst
iHcapable of reproduction, perform all the labours of the hive. The
office of continuing the race is restricted to the queen ; who is the
only perfect female in the community. If by any accident the queen
be destroyed, or if she be purposely removed for the sake of experi-
ment, the bees choose two or three from amongst the neuter eggSy
which have been deposited in their appropriate cells ; and these they
cause to be developed into perfect queens. The first operation is to
change the cells in which they lie into royal cells ; these differ con-
siderably from the ordinary ones in form, and are of much larger
dimensions. This is accomplished by breaking down the walls of
the surrounding cells, removing the eggs or grubs they may contain,
and rebuilding the central upon an enlarged scale, and upon the same
plan as the royal cells in which the queens are ordinjirily reared.
When the eggs are hatched, the maggot is supplied with food of a
very different nature from the farina or bee-bread (composed of a
mixture of pollen and honey) which has been stored up for the nourish-
ment of the workers : this food being of a jelly-like consistence and
pungent, stimulating character. After the usual transformations, the
grub becomes a perfect queen ; differing from the neuter bee, into
which it would otherwise have been changed, not only in the develop-
ment of the reproductive system, but in the general form of the body,
the proportionate shortness of the wings, the shape of the tongue,
jaws, and sting, the absence of the hollows on the thighs in which
the pollen is carried, and the loss of the power of secreting wax.

420. That insufficiency of wholesome food, continued through suc-
cessive generations, may produce a marked effect, not merely upon
the stature, but upon the form and condition of the body, even in the
Human race, appears from many cases, in which such influence has
operated on an extensive scale. Thus there are parts of Ireland
inhabited by a population descended from those who were treated
by the English as rebels two centuries since, and who were driven
into mountainous tracts, bordering the sea, where they have been
since exposed to the two great brutalizers of the human race,
hunger and ignorance. The present race is distinguished physically
from the kindred race of Meath and other neighbouring districts,
where the same causes have not been in operation, by their low stature
(not exceeding five feet two inches), their pot-bellies and bow-legs;
whilst their open projecting mouths, with prominent teeth and exposed
gums, their advancing cheek-bones and depressed noses, bear bar-
barism in their very front. " These spectres of a people that once
were well-grown, able-bodied, and comely, stalk abroad into the
daylight of civilization, the animal apparitions of Irish ugliness and
Irish want." — The whole aboriginal population of New Holland pre-
sents a similar aspect ; and apparently from the operation of the same
causes.

EFFECTS OF EXCESS OF FOOD. 251

421. When a larger quantity of food is habitually consumed than
the wants of the system require, it is not converted into solid flesh ;
but it is got rid of by the various processes of excretion. The in-
creased production of Muscular fibre depends, as we have already
seen (§ 362), upon nothing so much as the exercise of the muscle. It
cannot take place, unless the blood supply it with the materials : but no
degree of richness of the blood can alone produce it. Consequently,
the accumulation of nutritive matter in the blood is so far from being
a condition of healthy that it powerfully tends to produce disease, —
either of an inflammatory character, if the fibrin predominate, — or of
the hemorrhagic character, if the red corpuscles predominate. This
state is most apt to present itself in those who live well and take little
exercise ; and the remedy for it is either to diminish the diet, or to
increase the amount of exercise, so as to brfng the two into harmony.

422. The continued over-supply of food has several injurious effects;
it disorders the digestive processes, by stimulating them to undue
activity, and lays the foundation for a complete derangement of them ;
it gives a predisposition to the various diseases of repletion, as already
noticed ; and it throws upon the excreting organs much more than
their proper amount of labour, besides tending to produce a depraved
condition of the matters to be drawn off by them, which renders the
proper act of excretion still more difficult. When this is the case,
various disorders arise, caused by the retention, within the circulating
current, of substances which are very noxious to the general system,
and which become most fertile sources of disease. What are com-
monly regarded as diseases of the biliary and urinary organs, are
really, in a large proportion of cases, nothing else than disordered
actions of these organs, occasioned by the irregular mode in w^hich
the products of decomposition are formed within the blood, and de-
pendent upon some error in diet, either as regards quantity or quality.
Thus the " lithic acid diathesis," in which there is an undue propor-
tion of that substance in the urine, and of which Gout is a particular
manifestation, is due, not to disorder of the kidney, but to an undue
production of lithic acid in the blood ; so long as the excreting action
of the kidney is sufficient to prevent its accumulation in the blood, so
long the general health is but little affected ; but whenever that action
receives a check, various constitutional symptoms indicate that the
system is disturbed by the presence of this product of decomposition.
And though our remedies may be rightly directed, in part, to facili-
tating its escape through the kidneys, yet the radical cure is to be
sought only in the regulation of the diet, and in the prevention of the
first production of the substance in question. — Similar remarks might
probably be applied to disorders of the Liver; but we are, from
various causes, far less perfectly acquainted with their character than
we are with those of the Kidney.

423. There is only one tissue, the increase of which is directly
produced by an over-supply of food. This is the Adipose or fatty.
It is formed almost entirely at the expense of the non-azotized con"

252 INFLUENCE OF FOOD UPON PRODUCTION OF FAT.

stituents of the food ; the walls of the cells, into which the fatty
matter is secreted, being the only part of this tissue that is derived
from the proteine-compounds of the blood. The production of the
adipose tissue is most directly favoured by the presence of a large
amount of fatty matter in the food ; but it may also take place, as
will be presently shown, by the conversion of starchy and saccharine
substances into fatty compounds. It cannot occur, unless there be in
the food a larger proportion of substances that can be thus appro-
priated, than is sufficient to maintain the heat of the system by the
respiratory process. .Consequently, whatever increases the demand
for heat, is unfavourable to the deposition of fat; and vice versa. The
fattening of animals is now brought to a regular system ; and expe-
rience has shown that rest and a warm temperature, with food con-
taining a large amount of* oily matter, are most conducive to the accu-
mulation. Rest acts by keeping the respiration at a low standard ;
for it will hereafter be shown (Chap. VIII.), that a much larger pro-
portion of carbonic acid is thrown off when the body is in active
movement, than when it is in repose. External warmth has the same
effect; the demand upon the calorifying power being diminished, and
more of the combustible material being left, to be stored up as fat.

424. The deposition of fat affords a supply of combustible matter,
against the time when it may be needed ; and it is consequently found,
that the duration of life in warm-blooded animals, when they are com-
pletely deprived of food, is in great degree proportional to the amount
of fat they have previously accumulated. There is no sufficient
reason to believe that fatty matter can be converted, within the ani-
mal body, into a proteine-compound, which can serve for the nutri-
tion of the muscular and other tissues. But the greatest and most
constant waste, when an animal is undergoing starvation, is that which
is occasioned by the heat-producing process ; this, so long as the sup-
ply lasts, is kept up by the store of fat, which is gradually consumed ;
and when it is completely exhausted, the temperature falls, hour by
hour, until life can no longer be sustained, (§ 117). The use of this
store of fat, in supplying any temporary deficiency in the food, be-
comes evident from such experiments ; for when it has been com-
pletely exhausted, the withholding of a single meal proves fatal, from
the want of power to sustain the calorifying process. We find that
animals, which are likely to suffer from deficiency of food in the winter,
or which spend that period in a state of quiescence, have a tendency
to accumulate a store of fat in the autumn ; which tendency seems
principally to depend upon the nature of their food. We observe it
chiefly in those Birds and Mammals which live upon seeds and grains ;
and these, when ripe, contain a large quantity of oily matter, which
thus becomes a valuable store against the time of need. There are
many birds, such as the beccafico so much esteemed in Italy, which
are described, if killed at this season, as being " lumps of fat."

425. It is well known to breeders of cattle, that some varieties or
breeds have a much greater tendency to the production of Adipose

VALUE OF DIFFERENT MATERIALS OF FOOD. 253

tissue, than others placed under the same circumstances ; and the
former are therefore selected to undergo the fattening process. Cor-
responding differences may be met with among different individuals
of the Human race ; some persons having a remarkable tendency to
the production of fat, under circumstances which do not seem by any
means favourable to it, whilst others appear as much indisposed to this
deposit. The latter condition we notice particularly in that temperament
which is commonly termed the " bilious ;" and it is important to bear in
mind that, where such an indisposition exists, any superfluity of fatty
matter in the food taken into the system, must be excreted again through
the liver, instead of being retained and stored up in the body. It is
very desirable, therefore, that such persons should abstain from any
excess of this kind ; since an habitual call upon the liver, to relieve
the system of a superfluity of fatty matter, is certain to produce a dis-
ordered state of that organ; and in order to prevent it, the diet should
be altered so as to include less of fatty matter, or the amount of exer-
cise should be increased, so that it may be burned off by the addi-
tional respiration which then takes place.

426. We see, then, that the amount of food which can be properly
appropriated by the system varies considerably in different individuals,
and in the same individual under different circumstances. Conse-
quently it is impossible to give any general rule, which shall apply to
every one alike. The average quantity required by adult men, leading
an active life, and exposed to the ordinary vicissitudes of temperature
in our own climate, seems to be from 30 to 36 ounces of dry aliment.
But a healthy condition may be kept up on scarcely more than half
this allowance, if the muscular powers are but little exerted, and the
surrounding temperature be high; provided that it consist of sub-
stances of a nutritious kind, united in proper proportions.

427. The value of different substances as aliment, depends in the
first place upon the quantity of solid matter they contain ; being of
course the greater, as the solids form the larger proportion of the entire
weight. Many esculent vegetables contain so large a quantity of
water, that the nutriment they afford is very slight in proportion to
their bulk. — Next it depends upon the proportion of digestible matter
which the solid parts include ; for it is not every substance containing
the requisite ingredients, that is capable of being reduced to a state
which enables it to be absorbed. Thus woody fibre is composed of the
same elements as starch-gum ; but it passes out of the intestinal canal
unchanged, and therefore affords no nutriment. In the same manner,
the horny tissues of animals, though nearly allied to proteine in their
composition, are completely destitute of nutritive properties to Man
and the higher animals, because not capable of being reduced by their
digestive process; though certain insects appear capable of living
exclusively upon them.

428. But when the watery and indigestible parts of the food are
put out of consideration, and our attention is directed only to the
soluble solids, we find a most important difference in the chemical

254 VALUE OF DIFFERENT MATERIALS OF FOOD.

composition of different substances, -which renders them more or less
appropriate to the different purposes which have to be answered in the
nutrition of the body. It has been already pointed out, that Vege-
tables possess the power of combining the elements furnished by the
inorganic world into two classes of compounds, — the ternary, consist-
ing of oxygen, hydrogen, and carbon, — and the quarternary, which
consists of these elements, with the addition of azote or nitrogen.
These two classes are hence termed the non-azotized and the azotized.

429. Now the azotized compounds which are formed by Plants, are
essentially the same with those which are furnished by the flesh and
by the albuminous fluids of Animals, as already shown (§ 169); and
these are required for the reparation of the waste of the muscular
tissue and for the general nutrition of the body. Consequently, unless
the food contain a sufficient proportion of these substances, the body
must be insufficiently nourished, and the strength must diminish, even
though other elements of the food be in superabundance. The other
azotized compounds existing in the animal body may be elaborated
by the transformation of these proteine-compounds ; so that when they
are duly supplied, the system cannot become enfeebled for want of
support. — But there is another azotized compound, Gelatin, that is
furnished by Animals, to which nothing analogous exists in Plants ;
and this, although it cannot sustain life by itself, is a valuable adjunct
to the proteine compounds. For as the gelatinous tissues suffer waste
in common with the others, it is evident that if the gelatin be sup-
plied already prepared, it may be at once applied to their nutrition ;
and thus the proportion of proteine, which they would otherwise re-
quire, is not demanded, and the labour of transformation is also saved.
Further, there is this great advantage in combining a proportion of
gelatin with the food, — especially when the digestive powers are
feeble, — that being already in a state of perfect solution, it is taken up
at once by the simple act of physical absorption or endormose, instead
of requiring the selective absorption, which involves an act of cell-
formation (§ 494). But there is no evidence that gelatin can ever
be transformed into a proteine-corapound, and can thus be applied to
the nutrition of the muscular and other fibrous tissues ; and the pre-
sumption, derived from the results of various experiments, is very
strong the other way.

430. The quantity of azotized substances furnished by Plants is
usually small in proportion to that of the non-azotized ; being consider-
able only in the Corn-grains, and in the seeds of Leguminous plants,
which the universal experience of ages has demonstrated to be the
most nutritious of Vegetable substances. The non-azotized compounds
exist under various forms ; of which the principal are starch, sugar,
and oil. The two former may be regarded as belonging to one class ;
because we. know that starch and the substances allied to it maybe
converted into sugar by simple chemical processes, and that this trans-
formation takes place readily both in the Vegetable and Animal econo-
my. On the other hand, the oily matters contained in vegetable and

VALUE OF DIFFERENT MATERIALS OF FOOD. 255

animal food, are usually ranked as a distinct group of alimentary sub-
stances ; and it has been maintained that, under no circumstances, has
the Animal the power of elaborating fatty matter from starchy or sac-
charine cbmpounds. But this is now known to be an unfounded limi-
tation ; since the transformation of a saccharine into a fatty compound
takes place in the case of bees, which form wax when fed upon pure
sugar ; and it has been recently shown that it may take place in the
laboratory of the Chemist, butyric acid (the fatty acid of rancid butter)
being one of the products of the fermentation of sugar taking place
under peculiar circumstances.

431. The great use of these substances in the Animal economy, is
to support the respiratory process, and thus maintain the temperature
of the body. We have seen that, in the compounds of the Saccharine
group (in which Starch is included) the amount of oxygen is no more
than sufficient to form water with the hydrogen of the substance (§ 12);
so that the carbon is free to combine with the oxygen taken in by the
lungs, and thus becomes a source of calorifying power. Again, in
the oily matters taken in as food, the proportion of oxygen is far
smaller ; so that they contain a large quantity of surplus hydrogen,
as well as of carbon, ready to be burned off in the system, and thus
to supply the heat required. This is obviously the ordinary destina-
tion of the alimentary matters belonging to these classes ; and the
greatest economy in the choice of diet is therefore exercised, when it
is composed of azotized substances in sufficient amount to repair the
waste of the system, and of non-azotized compounds which include
free carbon and hydrogen in sufficient quantity to develop (with the
aid of other processes) the requisite amount of heat by combination
with oxygen. But if there be a deficiency in either of these kinds
of aliment, the body must suffer. Should the supply of duly-prepared
azotized matter be less than is required to repair the waste of the
albuminous and gelatinous tissues, then these diminish in bulk and
in vital power, though the heat of the body may be kept up to its
proper standard. But if the non-azotized matter would be supplied
in sufficient amount, or in a form in which it cannot be appropriated,
the heat of the body cannot be sustained in any other way than by
drawing upon the store of fat previously laid up.

432. Various circumstances lead to the belief, that the saccharine
compounds are thus carried off by the respiratory process, within a
short time after they have been introduced into the system. They
have not been detected in the chyle drawn from the lacteal absorbents ;
but there seems reason to believe that, in consequence of their ready
solubility, they are directly taken up by the blood (§ 493), and that
they are so rapidly burned off there, as to escape notice in that fluid.
But it has been lately shown by Dr. Buchanan, that, if the blood be
examined within a short time after a meal consisting in part of fari-
naceous and saccharine substances, a very appreciable quantity of
saccharine matter is found in it. This soon disappears, however ;
being eliminated or separated from the blood by the action of the

256 VALUE OF DIFFERENT MATERIALS OF FOOD.

lungs. In fact it is very probable, that a large proportion of the mat-
ter thus taken in never enters the general circulation at all ; as the
blood of the mesenteric veins proceeds to the lungs, after passing
through the liver, before it is transmitted to the systemic arteries, and
may there lose its saccharine matter, as fast as this is taken in from
the stomach. After a meal containing the ordinary admixture of sac-
charine, oily, and albuminous compounds, it is probable that the sac-
charine are first received into the blood, and are the first to be elimi-
nated from it ; and that, by the time they have been all consumed,
the oily matter, introduced through the more circuitous channel of the
lacteal system, is ready to answer the same purpose. If these are
exhausted before a fresh supply of food is taken in, cold as well as
hunger is experienced ; and the body is in this condition peculiarly
liable to suffer from any depressing causes, such as a low external
temperature, poisonous miasmata, &c.; hence the prudence of avoid-
ing exposure to such influences upon an empty stomach.

433. We can thus in part account for the fact, which universal
experience has established, that in warm-blooded animals, a mixture
of azotized and non-azotized substances is the diet most conducive
to the welfare of the body ; and that, in all but the purely carnivorous
tribes, the diet provided by Nature consists not only of albuminous,
gelatinous, and oily substances, such as are furnished by the flesh and
fat of animals, but also of saccharine or farinaceous matter. This is
the diet to which Man is evidently best adapted ; and it is remarkable
how completely accordant is his use of the ordinary materials of food,
"with the principles now established by chemical and physiological
research, in regard to the wants of his bodily system, and the best
mode of supplying them. Thus, good wheaten bread contains, more
nearly than any other substance in ordinary use, that proportion of
azotized and non-azotized matter, which is adapted to repair the
waste of the system, and to supply the necessary amount of combus-
tible material, under the ordinary conditions of civilized life in tem-
perate climates; and we find that the health and strength can be more
perfectly sustained upon that substance, than upon any other taken
alone. The addition of a moderate quantity of butter increases its
heat-producing powers ; and this is especially useful when the tem-
perature is low, — under which condition, there is usually an increased
disposition to the employment of fatty matters as articles of food. On
the other hand, if the body be subject to violent exertion, advantage
is gained by increasing the proportion of the proteine-compounds, by
the addition of animal flesh; and, under any circumstances, there is
an economy in the use of gelatin, in the form of soup, which dimin-
ishes the demand for other azotized matter. The use of animal
flesh, however, as a principal article of diet, except when the indi-
vidual is leading the incessantly-active life of a carnivorous animal,
is very far from being economical, and is positively injurious to the
welfare of the body.

434. On the other hand, in rice, potatoes, casava-meal, and simi-

VALUE OF DIFFERENT MATERIALS OF FOOD. 257

lar substances, the farinaceous or saccharine components form so very
large a proportion of the whole mass, and the proteine-compounds are
present in so very small an amount, that they are insufficient to sup-
port the bodily vigour when taken alone, unless a larger quantity be
ingested, so as to supply the requisite proportion of azotized matter.
But when these substances form part of a mixed diet, the other ingre-
dient of which consists of animal flesh, a much smaller quantity of
them suffices ; and the same kind of combination is then formed, as
exists in the single article of bread. Those in whose diet the farina-
ceous elements predominate largely, and the azotized compounds
exist in the smallest amount compatible with the maintenance of the
bodily vigour, are exempt from many diseases incident to those who
live more highly ; thus among the potato-eating Irish, and the oatmeal-
feeding Scotch, gout is a disease never heard of; whilst among the
richer classes of the same countries, there is no peculiar exemption
from it.

435. The oily constituents of food are most abundant in the diet
of the inhabitants of frigid zones, who feed upon whales, seals, and
other animals loaded with fat, and who devour this fat with avidity,
as if instinctively guided to its use. It is by the enormous quantity
of this substance taken in by them, that they are enabled to pass a
large part of the year in a temperature below that of our coldest win-
ter, spending a great portion of their time in the open air ; as well as
to sustain the extreme of cold, to which they are occasionally sub-
jected. And in consequence of its being more slowly introduced
into the system than most other substances, a larger quantity may be
taken in at one time, without palling the appetite ; whilst its bland
and non-irritating character favours its being retained until it is all
absorbed. In this manner, the Esquimaux and Greenlanders are
enabled to take in 20 or 30 pounds of blubber at a meal ; and, when
thus supplied, to pass several days without food. — On the other hand,
among the inhabitants of warm climates there is comparatively little
disposition to the use of oily matter as food ; and the quantity of it
contained in most articles of their diet is comparatively small.

436. In the Milk, which is the sole nutriment of young Mammalia
during the period immediately succeeding their birth, we find an ad-
mixture of albuminous, saccharine, and oleaginous substances; w^hich
indicates the intention of the Creator, that all these should be em-
ployed as components of the ordinary diet. The Casein or cheesy
matter is a proteine-compound ; the Butyrine of butter is but a slight
modification of its ordinary fats; and its sugar differs from that in
common use, only by its larger proportion of water. The relative
amount of these ingredients in the milk of different animals is subject,
as we shall hereafter see, to considerable variation ; but they con-
stantly exist, at least in the milk of the Herbivorous Mammalia, and
of those which, like Man, subsist upon a mixed diet. But it has been
recently asserted, that the milk of the purely Carnivorous animals is

17

258 IMPORTANCE OF VARIETY IN MATERIALS OF FOOD.

destitute of Sugar, consisting, like their food, of proteine-compounds
and fatty matter only.

437. No fact in Dietetics is better established than the impossibi-
lity of long sustaining health, or even life, upon any single alimentary
principle. Neither pure albumen nor fibrin, gelatin nor gum, sugar nor
starch, oil nor fat, taken alone for any length of time, can serve for the
due nutrition of the body. This is partly due, so far as the non-
azotized compounds are concerned, to their incapability of supplying
the waste of the albuminous tissues. This reason does not apply,
however, to the proteine-compounds; which can serve not only for the
reparation of the body, but can also afford .the carbon and hydrogen
requisite for the sustenance of its temperature. The real cause is to
be found in the fact, that the continued use of single alimentary sub-
stances excites such a feeling of disgust, that the animals experi-
mented on seem at last to prefer starvation, rather than the ingestion
of them. Consequently it is quite impossible to ascertain, by such
experiments, the nutritive power of the different alimentary princi-
ples ; no animal being capable of sustaining life upon less than two
of them at least. The same disgust is experienced by Man, when
too long confined to any article of diet, which is very simple in its
composition ; and a craving for change is then experienced, which
the strongest will is scarcely able to resist. Thus, in the treatment
of Diabetes, a disease in which there is an undue tendency to the
production of sugar in the system, it is very important to abstain
completely from the introduction of saccharine or farinaceous matters
in the food ; but the craving for vegetable food, which is experienced
when the diet has long consisted of meat alone, is such as to make
perseverance in the latter very diflficult; and a means has been latterly
devised of supplying this want without injury, by the use of bread
from which the starchy portion has been removed, the gluten or azo-
tized matter alone being eaten.*

438. The organic compounds, which have been enumerated as
supplying the various wants of the system, would be totally useless
without the admixture of certain inorganic substances, which also
form a constituent part of the bodily frame, and which are constantly
being voided by the excretions, especially in the Urine. These sub-
stances have various uses in the system. Thus common Salt, or the
Chloride of Sodium, appears to afford, by its decomposition, the mu-
riatic acid which is concerned in the digestive process, and the soda

• As an illustration of the advantage of this treatment, even in unpromising cases,
the Author may cite an instance which has come under his own observation. The
patient was a man 72 years of age ; the disease had lasted at least a year, and was
decidedly on the increase ; considerable loss of flesh and of muscular vigour had taken
place; and the quantity of sugar in the urine was such as to make it quite sweet to
the taste. By the careful restriction of his diet to animal flesh and gluten-bread, this
individual has kept the disease in complete check for more than 15 months ; he has
gained flesh, and improved in strength; and his urine is no longer sweet. Having
two or three times ventured upon a return to his ordinary diet, his old symptoms have
immediately manifested themselves, warning him of the necessity of perseverance in
the strict regimen prescribed for him.

NECESSARY MATERIALS OF ANIMAL FOOD. 259

which is an important constituent of the bile. Its presence in the
serura of the blood, also, and in the various animal fluids which are
derived from this, probably aids in preventing the decomposition of
the organic constituents of these fluids, — Phosphorus has been sup-
posed, until recently, to be chiefly requisite as one of the materials of
the nervous tissue (§ 383) ; and also, when acidified by oxygen, to
unite with lime in forming the bone-earth by which bone is consoli-
dated. But there is reason to believe, from the results of late inqui-
ries, that the acid and alkaline phosphate of lime and soda are very
important constituents of the various fluid secretions, and have a large
share in their respective actions. It has even been maintained that
the acid phosphate of lime is the essential ingredient in the gastric juice,
by which the first solutions of the food are effected. — Sulphur exists in
small quantities in several animal tissues; but its part appears to be
by no means so important as that performed by Phosphorus. — Lime is
required for the consolidation of the bones, and for the production of
the shells and other hard parts that form the skeletons of the Inverte-
brata ; and also as the base of the acid phosphate, which has been
just referred to as an important constituent of the animal fluids. —
Lastly, Iron is an essential constituent of Hsematosine ; and is conse-
quently required for the production of the red corpuscles of the blood
in Vertebrated animals.

439. These substances are contained, more or less abundantly, in
most of the articles generally used as food ; and where they are defi-
cient, the animal suffers in consequence, if they be not supplied in any
other way. — Thus, common Salt exists, in no inconsiderable amount,
in the flesh and fluids of animals, in the milk, and in the substance of
the egg; it is not so abundant, however, in Plants ; and the deficiency
is usually supplied to herbivorous animals in some other way. Thus,
salt is purposely mingled with the food of domesticated animals ; and
in most parts of the world inhabited by wild cattle, there are spots
where it exists in the soil, and to which they resort to obtain it. Such
are the *' bufifalo-licks" of North America. — Phosphorus exists also, in
combination with proteine-compounds, in all animal substances com-
posed of these ; and in the state of phosphate, combined with lime,
magnesia, and soda, it exists largely in many vegetable substances ordi-
narily used as food. The phosphate of lime is particularly abundant
in the seeds of the grasses ; and it also exists largely, in combination
with casein, in Milk. — Sulphur is also derived alike from vegetable
and animal substances. It exists, in union with proteine-compounds,
in flesh, eggs, and milk ; also in several vegetable substances ; and,
in the form of sulphate of lime, in most of the river and spring water
that we drink.

440. Lime is one of the most universally diffused of all mineral
bodies; for there are very few Animal or Vegetable substances in which
it does not exist. The principal forms in which it is an element of
Animal nutrition, are the carbonate and phosphate. Both these are
found in the ashes of the grasses, and of other plants used as food ;

260 MINERAL SUBSTANCES REQUIRED BY ANIMALS.

the phosphate of lime being particularly abundant (as already men-
tioned) in the corn-grains. The production of these cannot take
place, to their fullest extent, unless the soil previously contain phos-
phate of lime in a state in which the plant can receive it ; and it is
now understood, that the diminished fertility of many lands is due,
in great part, to the exhaustion of the soil as regards this ingredient.
The restoration of the alkaline and earthy phosphates to the soil, in
the form of manure, is the obvious means of preserving its fertility ;
but so long as a very large proportion of the excrements of animals
(the materials of which are originally derived from the earth, through
the vegetables it supplies), is allowed to run to waste, so long will it
be necessary that the requisite amount of phosphate of lime should
be drawn from foreign sources.

441. The phosphate of lime, as already mentioned, seems to per-
form important offices of a chemical nature in the animal economy,
besides being the chief solidifying ingredient of bones and teeth ; but
the carbonate would seem principally destined to mechanical uses
only; and we find it predominating, or existing as the sole mineral
ingredient, in those non-vascular tissues of the Invertebrated animals,
which give support and protection to their soft parts (§ 289). The
degree of development of these tissues depends in great part upon the
supply of carbonate of lime which the animals receive. Thus, the
Mollusca which inhabit the sea, find in its waters the proportion of
that substance which they require ; but those which dwell in streams
and fresh water lakes, that contain but a small quantity of lime, form
very thin shells ; whilst the very same species inhabiting lakes, which,
from peculiar local causes, contain a large impregnation of calcareous
wiatter, form shells of remarkable thickness. — The Crustacea, which
periodically throw off their calcareous envelop (§ 297), are enabled
to renew it with rapidity by a very curious provision. There is laid
up in the walls of their stomachs a considerable supply of calcareous
matter, in the form of little concretions, which are commonly known
as *' crabs' eyes." When the shell is thrown off, this matter is taken
up by the circulating current, and is thrown out from the surface,
mingled with the animal matter of which the shell is composed. This
hardens in a day or two, and the new covering is complete. The
concretions in the stomach are then found to have disappeared ; but
they are gradually replaced, before the supply of lime they contain is
again drawn upon. The large amount of carbonate of lime which is
required by the laying Hen, is derived from chalk, mortar, or other
substances containing it, which she is compelled by her instinct to
eat; and if the supply of these be withheld, the eggs which she
deposits are soft on their exterior, — not being destitute of shell, as
commonly supposed, — but having the fibrous element of the shell
(§ 181) unconsolidated by the intervening deposit of chalky particles.

SIMPLEST FORMS OF DIGESTIVE APPARATUS. 261

2. Of the Digestive Apparatus, and its Actions in general.

442. It has been already pointed out, that the nature of the food
of Animals is so far different from that of Plants, as to require the
preparatory process of Digestion, before its nutritious parts can be
taken up by the absorbent vessels and received into the system.
This process may be said to have three different purposes in view : —
the reduction of the alimentary matter to a fluid form, so that it
may become capable of absorption ; the separation of that portion of
it which is fit to be assimilated or converted into organized texture,
from that which cannot serve this purpose, and w^hich is at once
rejected; — and the alteration, to a certain extent when required, of
the chemical constitution of the former, which prepares it for the
important changes it is subsequently to undergo. The simplest con-
ditions requisite for the accomplishment of these purposes are the
following: — a fluid capable of performing the solution, and of effect-
ing the required chemical changes; — a fluid capable of separating
the excrementitious matter, by a process analogous to chemical pre-
cipitation ; — and a cavity or sac in which these operations may be
performed.

443. In the lowest Animals, we find this cavity formed upon a
very simple plan; the digestive sac being a mere excavation in the
solid tissue of the body, lined with a membrane which is an inverted
continuation of the external integument, and communicating with the
exterior by one orifice only, through which food is drawn in, and
excrementitious matter rejected. In the little Hydra, or fresh-water
Polype, the external covering of the body and the lining of the
stomach correspond so closely in their structure, — their actions dif-
fering only with their situation, — as to be mutually convertible ; for
the animal may be turned completely inside-out, without its functions
being deranged. The fluid necessary to dissolve the food, known by
the name of *' gastric fluid," or ** gastric juice," is secreted in the
walls of the stomach; and, from the transparency of the tissues, the
whole process may be watched. The prey is frequently, and indeed
generally introduced alive, by the contractile powder of the arms,
which coil round it, and gradually draw it into the mouth or entrance
to the stomach ; and its movements may often be observed to con-
tinue for some time after it has been swallow^ed. In a little time,
however, its outline appears less distinct, and a turbid film partly
conceals it; the soft parts are soon dissolved and reduced to a fluid
state ; and any firm indigestible portions which the body may con-
tain, are rejected through the aperture by which it entered. The
nutritive matter is absorbed by the walls of the stomach, every part
of which appears to be endowed with equal power in this respect ;
and it is conveyed to the remoter parts of the arms by the simple
imbibition of one part from another, without any proper circulation
through vessels.

444. In Polypes of a higher conformation, however, the digestive
cavity is provided with a second orifice ; from the dilated cavity or

262 VARIOUS FORMS OF DIGESTIVE APPARATUS.

stomach, an intestinal tube proceeds ; and this has a termination dis-
tinct from the mouth, though often in its neighbourhood. The food,
before entering the stomach, is submitted to a powerful triturating
apparatus, resembling the gizzard of birds, by which it is broken
down ; and in the digestive cavity it is submitted, not merely to the
action of the gastric fluid, but also to that of the bile, which is
secreted in little follicles in the walls of the stomach, and which is
poured into its cavity during the process of digestion, — being easily
recognized by its bright yellow colour. The excrementitious matter
is rejected in the form of little pellets, through the intestinal tube.

445. As we ascend the Animal scale, we find the digestive appa-
ratus gradually increased in complexity ; but its essential characters
remain the same. Near the entrance to the stomach, we usually find
an apparatus for effecting the mechanical reduction of the food, by
which its subsequent solution may be rendered more easy. This may
consist of a set of teeth ; either fixed in the mouth, as in Mammalia
and Reptiles ; or more particularly besetting the pharynx, as in
Fishes; or attached to the walls of the stomach, as in Crustacea.
Or it may be formed by the tongue, converted into a sort of rasp ; as
in the common Limpet, which thus reduces the sea-weeds that con-
stitute its chief food. Or the same purpose may be answered by a
gizzard, or first stomach, with dense muscular and tendinous walls;
such as we find in the grain-eating Birds, and many Insects, and in
certain Mollusks and Polypes. But where the food is already com-
posed of very minute particles, or is received in a liquid state, (as in
the case of those animals which live upon the juices of others,) or is
easily acted on by the gastric juice, no such preparation is requisite.

446. Before the food reaches the true digestive stomach, it is
sometimes delayed in a previous cavity, in order that it may be
macerated in fluid, and may be thoroughly saturated with it. This
is the purpose of the crop of Birds, and of the first stomach of Ru-
minant animals. When this incorporation with fluid is not effected
before the food is subjected to the triturating process, it usually takes
place concurrently with it ; and in those animals which reduce their
food in the mouth by the process of mastication, there is a special
secretion of fluid into that cavity for this purpose ; this fluid is termed
Saliva, and the act by which it is incorporated with the food is termed
insalivation. The mechanical reduction of the aliment, and its in-
corporation with fluid, constitute, as we shall hereafter see, a very
important preparation for the true digestive process.

447. This process, among higher animals, takes place exclusively,
or nearly so, in the stomach; the form of which varies with the cha-
racter of the food. When this is of a nature to be easily acted on by
the gastric fluid, the stomach is a simple enlargement of the aliment-
ary canal, almost in the direct line between the oesophagus and the
intestinal tube ; so that there is little provision for the delay of the
food in its cavity. But when the aliment is such as to be less easily
reduced, and requires to be submitted to the action of the gastric
fluid, for a longer period, the stomach forms a more considerable

VARIOUS FORMS OF DIGESTIVE APPARATUS.

263

enlargement, and is placed more out of the direct line between the
oesophagus and the commencement of the intestine. The former
condition obtains in the Carnivora, and particularly in those which
live more upon blood than upon flesh, — such as Weasels, Stoats, &c.,
in which this part of the alimentary tube is almost straight ; the latter
condition is found among the Herbivora, and the provision for the
delay of the aliment attains its greatest complexity in the Ruminant
animals. The form of the

Human stomach (Fig. 70) Fig. 70.

is intermediate between
that of purely carnivo-
rous and purely herbivo-
rous animals. As in the
former, there is a direct
passage from the cardiac
orifice or entrance of the
oesophagus, to the pyloric
orifice or commencement
of the intestine ; but there
is also a considerable di-
latation or cul de sac,
which is out of that line ;
and it appears that,
during the digestive pro-
cess, there is a constric-
tion across the stomach,
which separates the car-
diac portion from the py-
loric, and causes the re-
tention of the food in the
dilated part or large ex-
tremity. The gastric fluid
is still secreted in the
walls of this organ, by
scattered follicles which
pour their products into
its cavity through sepa-
rate orifices; but the bile is elaborated by a distinct organ, alto-
gether removed from it, which transmits its secretion by a single
duct, that opens into the intestinal tube at a short distance from its
commencement.

448. The action of the Stomach is restricted, in the higher animals,
to the reduction of the food by the solvent powers of the gastric juice,
and to the absorption (by the vessels in its walls) of those parts of it
which are in a state of the most perfect solution. The change which
is produced by the admixture of the bile, takes place in the intestine ;
and the principal part of the nutritive elements of the food are taken
up by the absorbent vessels of the walls of the intestine, after that
process has been accomplished. It would seem as if the preparation

A vertical and longitudinal section of the Human stomach
and duodenum, made in such a direction as to include the
two orifices of the stomach, 1. The oesophagus; upon its
internal surface the plicated arrangement of the cuiicular
epithelium is shown. 2. The cardiac orifice of the stomach,
around which the fringed border of the cuticular epithelium
is seen. 3. The great end of the stomach. 4. Its lesser or
pyloric end. 5. The lesser curve. 6. The greater curve.

7. The dilatation at the lesser end of the stomach, which has
received from Willis the name of antrum of the pylorus.
This may be regarded as the rudiment of a second stomach.

8. The rugae of the stomach formed by the mucous mem-
brane : their longitudinal direction is shown. 9. The pylo-
rus. 10. The oblique portion of the duodenum. 11. The

descending portion. 12. The pancreatic duct and the ductus
communis choledochus close to their termination. 13. The
papilla upon which the ducts open. 14. The transverse
portion of the duodenum. 15. The commencement of the
jejunum. In the interior of the duodenum and jejunum, the
valvulee conniventes are seen.

264 DIGESTIVE APPARATUS OF MAN.

of the food for absorption were not by any means completed, in this
first portion of the alimentary canal ; for it is still destined to pass
through a long and convoluted tube, which is sometimes extended
to an extraordinary degree ; and in this passage it is gradually ex-
hausted of its nutritious matter. The length of the intestinal canal
bears a close relation to the character of the food. In the Carnivorous
animals, whose aliment is easily dissolved and prepared for conver-
sion into blood, the intestine is comparatively short; thus in the Lion
and other Felines it is no more than three times the length of the
body ; and in some of the blood-sucking Bats,'it is almost straight and
simple. On the other hand, in Herbivorous animals it is of enor-
mous length ; thus in the Sheep it is about twenty-eight times as long
as the body. In animals whose diet is mixed, its length is inter-
mediate between these extremes ; thus in Man, the whole length of
the intestinal tube is about thirty feet, or between five and six times
that of the body. — The intestine is of much smaller diameter along its
first portion, than it is nearer its termination ; and it is consequently
distinguished into the small and the large. In the small intestine,
which constitutes in Man about five-sixths of the whole, the surface
of the mucous membrane is greatly extended by the valvulce conni-
ventes, which are folds or duplicatures, often several lines in breadth,
not entirely surrounding the intestine, but extending for about one-
half, or three-fourths of its circumference. These are wanting at the
lower part of the ileum. The whole surface of the mucous membrane
of the small intestine, below the entrance of the biliary ducts, is thickly
covered with villi, or little root-like projections, in which the proper
absorbent vessels originate. No proper valvulae conniventes exist in
the large intestine ; the only extensions of the raucous membrane
being crescentic folds at the edges of the sacculi or pouch-like dila-
tations in its walls ; and the villi are comparatively few in number,
gradually disappearing towards the termination of the intestine.

449. The mucous membrane of the alimentary canal, through its
whole course, is studded with the orifices of numerous scattered
glands, which lie in its thickness, or immediately beneath it. The
simplest of these are the follicles of Lieberkiihn, which are small
pouches, formed by an inflexion of the mucous surface, analogous to
the follicles of other mucous membranes, and
Fig. 71. apparently destined for the elaboration of the

protective secretion (§ 237, see Figs. 27 and
28). These follicles, in the small intestine, are
very simple in their character, and not very
deep ; and their apertures, which are small, are
situated for the most part around the bases of the
villi. In the large intestine they are more pro-
Mucous coat of smaii in- longed, especially towards the extremity of the
the 'fbuicies of Lieberkiihn icctum, whcrc they form a distinct layer, the
f^cviiTon^ ''"^''°"' ^^''^ component tubes of which are visible to the
naked eye ; they probably form the peculiarly
thick and tenacious mucus of that part. These mucous follicles

ALIMENTARY CANAL AND ITS MOVEMENTS. 265

become particularly evident when the membrane is inflamed ; for they
then secrete an opaque whitish matter, which is absent in the healthy
state, and which distinguishes their orifices (Fig. 71). — A modified
kind of these follicles, rather more complex in structure, is found
abundantly in the stomach; where it is concerned in the secretion of
the gastric fluid (§ 469).

450. The coats of the intestine contain other glandulse, which
appear destined, not so much to elaborate fluids of use in the system,
as to draw off* from the blood certain products of decomposition,
which are to be excreted from it. These are commonly known as
the glands of Brunner, and of Peyer, after the names of their respective
discoverers. — The glands of Brunner are situated in the duodenum,
and lie, not in the mucous but in the sub-mucous tissue. Though
their size is only about that of a hemp-seed, they are of very complex
structure, consisting of several hundred follicles, clustered round the
ramifications of an excretory duct, so as to resemble the Salivary
glands ; and each pours its secretion through a single orifice into the
intestinal tube. The glands of Peyer are either solitary ot agminated;
the latter form large patches, which are made up of aggregations of
the former. Each solitary gland consists of a closed spheroidal vesi-
cle, which is half imbedded in the mucous membrane, but which
also forms an elevated projection above it; and this projection is sur-
rounded by a ring or zone of openings, which lead into an annular
cluster of Lieberkiihnian follicles. On rupturing one of the Peyerian
vesicles, its cavity is found to contain a grayish-white matter, inter-
spersed with cells in various stages of development. The complete
closure of this cavity would seem to render it an exception to all
general rules of glandular structure ; but this is not so in reality ; for
it will be shown hereafter that many other glandular follicles in an
early stage of their development are equally closed (Chap. IX.); and
it appears that the Peyerian vesicles, when mature, discharge their
contents by an opening which then forms in the most projecting por-
tion of their walls, — these contents passing at once into the cavity of
the intestine, instead of being poured (as in other cases) into an
excretory duct. — Of the nature of the secretions of these intestinal
glandulse, nothing has been positively ascertained ; but some probable
inferences from well-known facts will be stated hereafter (Chap. XI).

3. Movements of the Alimentary Canal,

451. The food which is conveyed to the mouth, is grasped with
the lips, by a muscular eflfort, which is voluntary in the adult under
ordinary circumstances, but which may be performed instinctively
when the influence of the will is withdrawn ; in the infant, as among
the lower animals, the action seems purely instinctive, the nipple of
the mother being firmly grasped by the lips when introduced between
them, even after the brain has been removed. — By the act of masti-
cation, which then succeeds, the food is triturated and mingled with

266 MASTICATION.

the salivary secretion ; and is thus prepared for the further process of
solution, to which it is to be subjected in the stomach. The degree
of this preparation, and the form of the instruments by which it is
effected, vary in different animals, according to the nature of the food.
In those Carnivora, whose aliment consists exclusively of flesh, very
litde mastication is necessary, because this substance is very readily
acted on by the gastric fluid ; and we accordingly find the molar teeth
raised into sharp cutting edges, and working against each other with
a scissors-like action (the only one permitted by the articulation of the
jaw), so as simply to divide the food. On the other hand, in those
Herbivora, whose food consists of tough vegetable substances, such
as the leaves of grasses, or the stems and roots of other plants, we
find the molar or grinding teeth peculiarly adapted to its reduction ;
their surface being extended horizontally, and being kept continually
rough, by the alternation of vertical plates of different degrees of
hardness; and the lower jaw being so connected with the skull, that
great freedom of motion is permitted. In Man we find an inter-
mediate conformation, as regards both the teeth and the articulation
of the jaw; for the molar teeth possess broad surfaces, which are
covered with a continuous coat of enamel, but which are raised into
rounded tubercles; and the articulation of the jaw allows it a degree
of freedom, which is much greater than that possessed by the Carni-
vora ; although inferior to that which exist in many Herbivora. The
whole apparatus of Mastication is so formed in Man, as to lead to the
conclusion that he is destined to live on a mixed diet, composed in
part of animal flesh, and in part of vegetable substances that are
sufficiently soft to be reduced by the simple act of crushing, or by the
slight trituration for which the molar teeth are adapted.

452. The mechanical reduction of the food by Mastication, and
the incorporation of the Salivary secretion with its substance, consti-
tute a very important step in the Digestive process. We shall here-
after see that the operations, to which the alimentary matter is
subjected in the stomach, are of a purely Chemical nature ; and this
preparation is exactly of the same character as that which the Chemist
finds it advantageous to make, when he is operating on a substance
of difficult solution. For nothing is so favourable to the action of
the solvent, as the previous reduction of the matter to be dissolved,
and its thorough incorporation with the fluid that is to act upon it.
We shall hereafter see, that the relative properties of the Saliva and
of the Gastric fluid are such, that, by the minute admixture of the
food with the former, the latter finds access to every particle of it.
Hence the practice of eating so rapidly, that Mastication and Insali-
vation are insuflSciently performed, is extremely injurious; since it
throws more work upon the Stomach than it ought to perform, by
rendering its solvent action more difficult. There can be no doubt
that, by the prolonged continuance of it, a foundation is laid for the
distressing complaint termed Dyspepsia, or difficulty of digestion ; and
where any form of this complaint exists, too much attention cannot
be paid to the efficient reduction of the food in the mouth.

ACT OF DEGLUTITION. 267

453. When the aliment has been sufficiently triturated, it is con-
veyed into the Pharynx by the act of Deglutition or swallowing. This
act involves a great many distinct movements, into a minute descrip-
tion of which we shall not here enter ; but it is desirable that its
general nature should be well understood. It is one of those most
purely reflex in its character (§ 394), and is not capable of being per-
formed or even controlled by a voluntary effort. This statement may
seem inconsistent with the fact, that we swallow when we will ; but
it is not so in reality. The muscular movements which are concerned
in deglutition, are excited by nerves that proceed from the spinal cord,
not from the brain ; these motor nerves are excited to action, by the
contact of solid or fluid matters with the mucous surface of the fauces,
— and in no other way. The impression produced by the contact is
conveyed to the medulla oblongata, or that portion of the spinal cord
which lies within the cranium, by afferent nerves that terminate in
it; and, in immediate respondence to that impression, a motor impulse
is transmitted from it, which calls the muscles into the combined action
necessary to produce the movement. Now this contact a/50 produces
a sensation, provided the brain be sound and awake, because nervous
fibres proceed from the mucous surface to the brain as w'ell as to the
spinal cord ; but this sensation is not a necessary link in the chain of
actions, by which the movement is produced ; for the act of Degluti-
tion takes place during profound sleep, when all sensation is suspended,
and it may be excited even after the brain has been removed. It
seems to be voluntary, under ordinary circumstances, simply because
it is by an act of the will, that the matter to be swallowed is carried
backwards into contact with the fauces ; but that it is not so in reality,
is shown by the fact, that when this impression has once been made
with sufficient force, we cannot by any effort of the will, prevent the
action. We have a good example of this in the following circum-
stance, of no very unfrequent occurrence. The tickling of the upper
part of the fauces with a feather is often practised to induce vomiting ;
but if the end of the feather be carried too far down, it excites the
act of deglutition instead ; the feather is grasped by the pharynx and
drawn downwards; and if it be not held tenaciously between the
fingers, it is drawn from them and carried dow^nwards into the sto-
mach.

454. The carrying-back of the alimentary matter, so that it reaches
the fauces or upper part of the pharynx, is principally accomplished
by the tongue ; when it has passed the anterior palatine arches, these
contract and close over the tongue, so as to prevent the return of the
food into the mouth ; and at the same time the posterior palatine arches
and the uvula are so drawn together, as to prevent its passage into
the posterior nares. The larynx is drawn forwards beneath the root
of the tongue, and the epiglottis is pressed down over the rima glot-
tidis, so that nothing can enter the latter, unless drawn towards it by
an act of inspiration. When fairly within the pharynx, the alimentary
matter is seized by the constrictors which enclose that part of the ali-

268 MOVEMENTS OF (ESOPHAGUS.

mentary tube, and is drawn downwards by them into the oesophagus,
which is the cylindrical continuation of it. The continued action of
the constrictors serves to propel the food along the oesophagus ; their
movement being of a reflex nature, excited by the contact of the sub-
stance contained in the tube, with its lining membrane, — which pro-
duces an impression that is transmitted to the medulla oblongata, and
is reflected back as a motor impulse to the muscles. We have here
a distinct case of reflex action without sensation ; for we have no
consciousness of the ordinary passage of food down the oesophagus,
unless it occasion pressure on the surrounding parts through its bulk,
or unduly irritate the lining membrane by its high or low temperature
or its acrid qualities ; and yet it may be shown by experiment, that
the completeness of the nervous circle is requisite for the excitement
of the movement, which will not take place when it is interrupted
either by division of the nerves, or by destruction or paralysis of the
medulla oblongata.

455. The progress of the food along the (Esophagus is aided by
the action of the muscular coat peculiar to it. This is composed of
the non-striated fibre ; and, like that of the intestinal canal further
on, it is usually stimulated to contraction by the direct contact of the
stimulus, and not either by the will, or by the reflex action of the
spinal cord. The movement produced by it is of the peristaltic or
wave-like kind ; the contractions being limited to one portion of the
tube, and being propagated along it from above downwards. This
action continues after the division of all the nerves supplying the
oesophagus ; and it cannot, therefore, be dependent upon the brain or
spinal cord. It may be observed to take place in a rhythmical man-
ner (that is, at short and tolerably regular intervals), whilst a meal is
being swallowed; but as the stomach becomes full, the intervals are
longer and the wave-like contractions less frequent. The degree in
which the action of the oesophagus alone, without that of the sur-
rounding muscles, is capable of propelling the food into the stomach,
seems to vary in different animals. When the latter are paralyzed in
the Dog, by section of the nerves that supply them, the food that has
entered the oesophagus is still propelled into the stomach ; but this is
not the case in the Rabbit, the action of its oesophageal fibres not
being sufficient to carry the food onwards to the stomach, though it
will expel it from the divided extremity of the tube when it is cut
across. The usual peristaltic movements of the oeosophagus are re-
versed in Vomiting; and this reversion has been observed, even after
the separation of the stomach from the oesophagus, as a consequence
of the injection of tartar emetic into the veins.

456. At the point where the oesophagus enters the Stomach, — the
cardiac orifice of the latter, — there is a sort of sphincter, or circular
muscle, which is usually closed. This opens when there is a suffi-
cient pressure on it, made by the accumulated food propelled by the
movements of the oesophagus above ; and it then closes again, so as
to retain the food in the stomach. The closure is due to reflex ac-

TERMINATION OF OESOPHAGUS IN RUMINANTS. 269

tion; for when the nerves supplying it are divided, the sphincter no
longer contracts, and the food regurgitates into the oesophagus. The
opening of the cardiac is one of the first acts which takes place in
vomiting.

457. In Ruminating animals, there is a very remarkable conforma-
tion at the lower end of the oesophagus, which is destined to regulate
the passage of food into the different compartments of the stomach,
according as it has been submitted to the second mastication, or not.
The oesophagus does not terminate at its opening into the first stomach
or paunch, but it is continued onwards as a deep groove with two lips
(Fig. 73) : by the closure of these lips it is made to form a tube, which
serves to convey the food onwards into the third stomach ; but when
they separate, the food is allowed to pass either into the first or the
second stomachs. When the food is first swallowed, it undergoes but
very little mastication ; it is consequently firm in its consistence, and
is brought down to the termination of the oesophagus in dry bulky
masses. These separate the lips of the groove or demi-canal, and pass
into the first and second stomachs. After they have been macerated
in the fluids of these cavities, they are returned to the mouth by a

Fig. 72.

Stomach of Sheep ;— a, cEsophagus ; b, paunch ; c, second, or honeycomb stomach ; d, third stomach,
or many-plies j e, fourth stomach or reed; /, pylorus.

reverse peristaltic action of the oesophagus; this return takes place in
a very regular manner, the food being shaped into globular pellets by
compression within a sort of mould formed by the demi-canal, and
these pellets being conveyed to the mouth at regular intervals, appa-
rently by a rhythmical movement of the oesophagus. It is then sub-
jected to a prolonged mastication within the mouth (the ** chewing of
the cud"), by which it is thoroughly triturated and impregnated with
saliva ; after which it is again swallowed in a pulpy semi-fluid state.
It now passes along the groove which forms the continuation of the
oesophagus, without opening its lips ; and is thus conveyed into the
third stomach, whence it passes to the fourth, in which alone the true
digestive process takes place. Now, that the condition of the food
as to bulk and solidity, is the circumstance which determines the
opening or closure of the lips of the groove, and which consequently
occasions its passage into the first and second stomachs, or into the
third and fourth, appears from the experiments of Flourens; who
found that when the food, the first time of being swallowed, was arti-

270

MOVEMENTS OF THE STOMACH.

Fig. T3.

ficially reduced to a soft and pulpy condition, it passed for the most
part along the demi-canal into the third stomach, as if it had been
ruminated, — only a small portion finding its way into the first and
second stomachs. How far the actions of this curious apparatus are
dependent upon nervous influence, — or how far they are due to the
exercise of the contractility of the muscular fibre, directly excited by
the contact of the substances with the lining membrane of the tubes
and cavities, — has not yet been clearly ascertained.

458. The food, when introduced into the Stomach, and submitted
to the solvent action of its secretions, is also subjected to a peculiar

movement, which is eflfected by
the muscular walls of that organ.
The purpose of this motion is
obviously to keep the contents
of the stomach in that state of
constant agitation, which is most
favourable to their chemical so-
lution ; and particularly to bring
every portion of the alimentary
matter into contact with the walls
of the stomach, so as to be sub-
jected to the action of the fluid,
which is poured forth from them
during the digestive process.
The movement is produced by
the alternate shortening and re-
laxation of the various fasciculi,
which are disposed in almost
every direction throughout the
muscular wall of the stomach ;
and it seems to produce a kind
of revolution of the contents of
the stomach, sometimes in the
direction of its length, and some-
times transversely. Its result is
well shown in the hair-balls,
which are occasionally found in
the stomachs of animals, that
have swallowed hair from time
to time through licking their
skins ; the component hairs not
being pressed together confusedly, but being worked together in
regular directions, and so interwoven that they cannot be readily
separated. As digestion proceeds, the dissolved fluid escapes, little
by little, through the pyloric orifice, which closes itself firmly against
the passage of solid bodies ; and this motion continues, until the sto-
mach is completely emptied ; when it ceases, until food is again in-
troduced. The bulk of the alimentary mass diminishes rapidly, as

Section of part of the Stomach of the Sheep, to
show the demi-canal of the oesophagus ; the mucous
membrane is for the most part removed, to show the
arrangement of the muscular fibres. At a is seen
the termination of the ossophageal tube, the cut edge
of whose mucous membrane is shown at b. The
lining of the first stomach is shown at c^c; and the
mucous membrane of the second stomach is seen
to be raised from the subjacent fibres at d. At e, e,
the lips of the demi-canal are seen bounding the
groove, at the lower end of which is the entrance
to the third stomach or many-plies.

MOVEMENTS OF THE INTESTINAL CANAL. 271

the solvent process is near its completion ; and the separation of the
fluid product or chyme is aided by a peculiar action of the transverse
fasciculi, which surrounds the stomach at about four inches from its
pyloric extremity. These shorten in such a manner, as to produce a
sort of hour-glass separation between the portions of the stomach on
either side of it ; and the fluid solution, being received by the pyloric
or smaller portion, is pumped away through the pylorus ; whilst the
solid matter yet undissolved is retained in the larger division.

459. The degree in which these movements are dependent upon
the nervous system, or are under its control or direction, has not yet
been clearly ascertained. Distinct movements may be excited in the
stomach of a Rabbit, if it be distended with food, by irritating the
par vagum soon after the death of the animal ; these movements
seem to commence from the cardiac orifice, and then to spread them-
selves peristaltically along the walls of the stomach ; but no such
movements can be excited if the stomach be empty. On the other
hand, there is distinct proof, that all the movements necessary to di-
gestion may take place after the section of that nerve ; although the
first effect of the operation appears to be to suspend them completely.
It is probable that the movements of the stomach are more regular
and energetic in Herbivorous animals, whose food is difficult of di-
gestion, than they are in the Carnivora, whose aliment is dissolved
with comparative facility.

460. From the time that the ingested matter enters the Intestinal
tube, it is propelled onwards by the peristaltic contractions of its mus-
cular coat ; which are excited, independently of all nervous influence,
by the contact of the aliment, or by that of the secretions mingled
with it in its passage along the canal. These last appear to have an
important effect ; for we find that, when the bile-duct is tied, so as to
prevent the bile from entering the intestine, constipation always oc-
curs ; whilst an increase of the biliary and other secretions, consequent
upon the action of mercury or upon any other cause, produces an
increased peristaltic movement, and a more rapid discharge of the
excrementitious matter. During the passage of the alimentary matter
along the small intestine, as we shall see hereafter, a large proportion
of its fluid is removed, by the absorbent power of the villi ; and the
residue is again brought, therefore, to a more solid consistence. This
residue consists in part of those portions of the aliment, which are
not capable of being dissolved or finely divided, so as to be received
by the absorbents ; and in part of the matters poured into the ali-
mentary canal, by the various glands that discharge their contents into
it, for the purpose of being carried out of the body. The feces,
which are thus formed, are propelled through the large intestine, by
the continued peristaltic action of its walls, until they arrive at the
rectum.

461. That the ordinary peristaltic action of the intestinal canal is
independent of nervous influence, is suflficiently proved by the fact,
that it will continue when the tube is completely separated from all

272 DEFECATION.

connection with the nervous centres; as well as by the difficulty,
already adverted to (§ 353), of exciting contractions in the muscular
coat by any stimulation of its nerves. All the nerves of the intestine,
from its commencement at the pyloric orifice of the stomach to its ter-
mination at the anus, are derived from the ganglia of the sympathetic
system ; but there is evidence that those which influence its movements
are really derived from the spinal cord (see Chap. XII). Although
the will has no influence whatever on the peristahic movement, yet
the emotions seem to affect it ; and it is probably to convey their influ-
ence that the intestinal canal is supplied with motor nerves. It is
also furnished with sensory nerves, which form part of the trunks of
the sympathetic system, but which really pass onwards to the brain;
these do not, however, make us conscious of the passage of the ali-
mentary matter along the canal, so long as it is in a state of health ;
but in various diseased conditions, they give rise to sensations of the
most painful nature.

462. For the occasional discharge of the feces from the rectum, and
for the retention of them at other times, we find the outlet or anal
orifice, provided with an additional muscular apparatus, which is con-
nected with the spinal system of nerves. The act of defecation is due
tothe pressure upon the contents of the rectum, which is occasioned by
the combined contraction of the diaphragm and the abdominal muscles;
whilst, on the other hand, the retention of the feces is due to the con-
tractile power of the sphincter muscle, which surrounds the anus. The
action of the sphincter ani, like that of the sphincter of the cardia, is a
reflex one; dependent upon the connection of the muscle, by excitor
and motor nerves, with the spinal cord. If the lower portion of the cord
be destroyed, or if the nerves be divided, the sphincter loses its con-
tractile power, and becomes flaccid. When in proper action, however,
its power is sufficient to prevent the escape of the contents of the rec-
tum ; until the expulsive force becomes very strong, in consequence
either of the quantity of feces which has accumulated, or the acridity
of their character. In either case, the impression made upon the mu-
cous membrane of the rectum is conveyed to the spinal cord ; and, by
a reflex motor impulse, the muscles of defecation are thrown into com-
bined action, the resistance of the sphincter is overcome, and the feces
are expelled. An unduly irritable state of the mucous membrane, or
a disordered state of the excrementitious matter (resulting from the
irritating character of the substances swallowed, from the acrid charac-
ter of the secretions poured into the canal, or from an unusual change
in the aliment during the digestive process), may occasion unduly fre-
quent calls upon the muscles of defecation, which the sphincter is
unable to resist. On the other hand, if the progress of the feces be
delayed in the large intestines, by deficient peristaltic movement, they
accumulate higher up, and the act of defecation is not excited.

463. Although the sphincter ani on the one hand, and the muscles
of defecation on the other, are called into action by the reflex power
of the spinal cord, and are so far involuntary in their operation, yet
they are also in some degree subject (in Man at least) to the influence

MUCOUS SECRETION. 273

of the will. The resistance of the sphincter may be increased by a
voluntary effort, when it is desired to retain the feces in opposition to
the power of the expulsors; and it is only when the latter operate
with excessive force that they can overcome it. On the other hand,
the expulsors may be called into action, or maybe aided, by the will,
when the stimulus to their movement received through the spinal cord,
would not otherwise be strong enough ; and the feces may thus be
evacuated by a voluntary effort, at a time when they would not other-
wise be discharged.

4. Of the Secretions poured into the Alimentary Canal, and of Changes
which they effect in its contents,

464. The whole Mucous Membrane of the Alimentary canal, from
the mouth to the anus, is covered during health with that peculiar
viscid secretion termed mucus, of which the characters have been
already described (§ 237). This is formed, partly, on the free sur-
face of the membrane itself, but chiefly in the numerous follicles or
depressions by which that surface is increased ; and it appears de-
stined for the protection of the delicate, highly vascular membrane
from undue irritation by the contact of the substances, which are passing
through the alimentary tube. When these are unusually acrid, the
secretion of mucus is augmented in quantity, and is increased in vis-
cidity, so as to form an effective sheath to the membrane, which would
otherwise suffer severely. When this secretion is deficient, the mem-
brane is irritated by the contact of any but the blandest substances ;
and the class of remedies termed demulcents are useful in coating and
protecting it.

465. During the mastication of the food in the mouth, the Salivary
secretion is poured in, for the purpose of being mingled with it, and of
rendering the act of mastication more easy. This secretion is formed
by three pairs of glands, — the Parotid, the Sub-lingual, and the Sub-
maxillary; these are composed of minute

follicles, whose diameter is about 1-lOOOth Fig. 74.

of an inch, connected together by branches
of their ducts, upon which they are set like
grapes upon their stalk, surrounded by a
plexus of blood-vessels, and bound together
by areolar tissue. Within the follicles are
the true secreting cells (§ 238); by whose
growth and development, the material of the
secretion is separated from the blood. These
salivary cells are often to be recognized in
the saliva; they must not, however, be con-
founded with the epithelium cells of the
mucous membrane of the mouth, which are Lobuie of Parotid Giand of
much larger. The fluid obtained from the "^Z^^^'i^Z"
mouth is not pure saliva ; for the mucus of
18

274 SALIVARY GLANDS AND THEIR SECRETIONS.

the mouth itself is mingled with the secretion from the salivary
glands. If the proportion of the former be considerable, it gives to
the fluid of the mouth an acid reaction ; whilst if the latter be pre-
dominant (which it is directly before, and during the act of eating),
the fluid of the mouth has an alkaline reaction. It may be some-
times observed, that the saliva of the mouth will strike a blue colour
with reddened litmus paper, whilst it turns blue litmus paper red ;
thus showing the presence both of an acid and an alkali in a state of
imperfect neutralization.

466. The solid matter of the Salivary secretion is about 1 per cent,
of the whole ; and this consists in part of animal principles, and in
part of saline substances. The animal matter consists of osmazome,
mucus, and a peculiar substance termed ptyaline or salivary matter ;
which is soluble in water and insoluble in alcohol, and which is yet
different from both albumen and gelatin. This substance appears to
have a decided effect in producing the metamorphosis of certain ali-
mentary substances, on which it acts like 2i ferment. Starch may be
converted into sugar, and sugar into lactic acid, by its agency ; and,
if concentrated, it has a certain solvent power for casein, animal
flesh, and other proteine-compounds. Its chemical nature has not
yet been precisely determined. The saline constituents of the Saliva
are nearly identical with those of the blood ; the chlorides of sodium
and potassium form considerably more than half; and the remainder
consists chiefly of the tribasic phosphate of soda, to which the alka-
line reaction of the fluid is due, with the phosphates of lime, magnesia,
and iron. It is of the earthy phosphates, that the tartar which col-
lects about the teeth is chiefly composed ; the particles of these being
held together by about 20 per cent, of animal matter: and the compo-
sition of the concretions, which occasionally obstruct the salivary
ducts, is nearly the same.

467. The quantity of Saliva formed during the twenty-four hours,
has been estimated at from 15 to 20 ounces ; but on this point it is
impossible to speak with certainty. The secretion is by no means
constantly flowing; indeed it is almost entirely suspended, when the
masticator muscles and tongue are at perfect rest, unless it be excited
by any mental cause ; and hence it is, that the mouth becomes dry
during sleep, if it be not kept closed. The flow of Saliva takes place
just when it is most wanted; that is, w^hen food has been taken into
the mouth, and when the operation of mastication is going on. But
it will also take place, especially in a hungry person, at the sight, or
even at the idea, of savoury food ; as is implied by the common ex-
pression of the " mouth watering" for such an object. The influence
thus exercised over it by the emotional state of the mind, is probably
conveyed to the salivary glands by the Fifth pair ; which contains
many of the gray or organic filaments ; and which seems to take the
place, in the Head, of a distinct lymphatic system.

468. Having been conveyed into the Stomach, the food is sub-
mitted to the action of the Gastric Fluid, which is secreted in the

GASTRIC FOLLICLES AND THEIR SECRETION.

275

walls of that organ. This fluid is not present in the empty stomach ;
its secretion being excited by the presence of food, or by the irritation
of the walls of the organ by some solid body. In the intervals be-
tween the digestive process, the mucous membrane is of a light pink
hue; but it becomes more turgid with blood, when the presence of
food calls for the activity of its secreting processes. It is of a soft
and velvet-like appearance ; and it is constantly covered with a very
thin transparent viscid mucus, which has neither acid nor alkaline
reaction. By applying aliment or other stimulants to the internal coat
of the stomach, and by observing the effect through a magnifying
glass, numerous minute papillae can be seen to erect themselves upon
the mucous membrane, so as to rise through the coating of mucus ;
and from these is poured forth a pure, limpid, colourless, slightly
viscid fluid, having a distinctly acid reaction, which is the Gastric
juice. This fluid is secreted by follicles, which are lodged in the
walls of the stomach, and which closely resemble those that else-
where secrete mucus ; but they are usually of more complex structure,
and are more numerous.

469. If the Mucous Membrane of the stomach be divided by a
section perpendicular to its walls, it is seen to be made up, as it were^
of tubular follicles closely applied to each other ; their blind extremi-
ties resting upon the submucous tissue, and their open ends being di-
rected towards the cavity of the stomach. In some situations, these
tubuli are short and straight ; in other parts they are longer, and
present an appearance of irregular dilatation or partial convolution
(Fig. 75, 1). This is their usual character, especially near the car-
diac orifice of the stomach ; but near the pyloric orifice they have a
much more complex structure (Fig. 75, 2). These tubular follicles-
are arranged in bundles or groups, and are surrounded and bound

Fig, 75.

Fig.

Glandulac from the coats of the stomach, magnified 45
diameters; — 1, from the middle of the stomach; 2, from
the neighbourhood of the pylorus.

Portion of the mucous mem-
brane of the stomach, showing
the entrances to its secreting
tubes, in pits upon its surface.

together by a fine areolar membrane ; and this also serves to convey
vessels from the submucous tissue, which ramify among the follicles,
and supply the materials for their secretion. The number of tubuli
in each group is by no means constant. The follicles do not, in
general, open directly upon the surface ; but into the bottom of small

276 PROPERTIES OF GASTRIC FLUID AND OF PEPSINE.

depressions or pits, which may be seen to cover the membrane.
These pits are more or less circular in form ; and are separated from
one another by membranous partitions, which vary in depth, and some-
times by pointed processes, which are capable of erecting themselves
in the manner just described. The diameter of these pits varies
from about 1- 100th to l-250th of an inch ; it is always greatest near
the pylorus. The number of the gastric follicles opening into each,
is usually from three to five ; but there are sometimes more.

470. The chemical composition of the Gastric fluid has been a sub-
ject of much discussion, and can scarcely yet be regarded as deter-
mined. Possibly it may vary in its nature, according to the state of
the system, and the kind of animal from which it is obtained. That
of Man has been usually stated to contain a sensible quantity of un-
combined Muriatic and Acetic acids, to which its acid reaction has
been attributed ; whilst, on the other hand, it has been recently as-
serted, that the gastric fluid of the Dog contains no free muriatic acid,
and that its acid reaction is due to the presence of the superphosphate
of lime. The other inorganic ingredients of the Gastric fluid are
Eearly the same as those of the Saliva. It contains a peculiar organic
compound, which, like Ptyaline, bears a considerable resemblance to
albumen, but which is not identical with it ; to this the name of Pep-
sine has been given. The properties of Pepsine have been principally
studied in that form of it obtained from the mucous membrane of the
stomach of the Pig, which bears a close resemblance to that of Man.
When this membrane is digested in a large quantity of warm water,
it is purified from the various soluble substances it may contain ; but
the pepsine is not taken up, as it is not soluble in warm water. By
continuing the digestion in cold water, the pepsine is then extracted
nearly pure. When this solution is evaporated to dryness, there re-
mains a brown, grayish, viscid mass, having the appearance of an
extract, and 'the odour of glue. A similar substance may be obtained
by adding strong alcohol to a fresh solution of pepsine ; for the latter
is then precipitated in white flocks, which may be collected on a filter,
and which produce a gray compact mass when dried. Pepsine enters
into chemical combination with many acids; forming compounds
which still ;Fedden litmus paper ; and this appears to be its condition
in the gastric juice.

471. The (muriate ;and acetate of pepsine possess a very remarkable
solvent power for albuminous substances. A liquid which contains
only 17 ten-thousandths of acetate of pepsine, and 6 drops of muriatic
acid per ounce, possesses solvent power enough to dissolve a thin
slice of coagulated albumen, in the course of six or eight hours' diges-
tion. With 12 drops of muriatic acid per ounce, the same quantity
of white of egg is dissolved in two hours. A liquid which contains
only half a grain of acetate of pepsine, and to which muriatic acid and
white of egg are alternately added, so long as the latter is dissolved,
is capable of taking up 210 grains of coagulated white of egg, at a
temperature between 95^ and 104.° The same acid with pepsine

ACTION OF GASTRIC FLUID— CHYME. 277

dissolved blood, fibrin, meat, and cheese; whilst the acid without
the pepsine requires a very long time to do so at ordinary temperatures.
Very dilute muriatic acid, however, at the boiling point, dissolves
these albuminous substances ; and the solution has the same charac-
ters as that which is made by the agency of pepsine. The horny
tissues, — such as the epidermis, horn, hair, &c., — and the yellow
fibrous tissue, are not affected by the acid solution of pepsine. It
appears from these experiments, that the muriatic acid is the real
solvent ; and that the action of the pepsine is limited to disposing the
albuminous matter for solution, producing in it a change analogous to
that which may be effected by heat. Hence it may be considered,
like ptyaline, as a sort o{ ferment ; its office being to produce a tend-
ency to change, in the substances on which it acts, without itself
entering into new combinations with any of their elements.

472. These experiments appear to afford an explanation of the
properties of the gastric fluid, as ascertained by direct experiment
upon it. When drawn direct from the human stomach, it is found to
possess the power of dissolving various kinds of alimentary substances,
whilst these are submitted to its action at a constant temperature of
100° (which is about that of the stomach), and are frequently agitated.
The solution appears to be in all respects as perfect as that which
naturally takes place in the stomach ; but a longer time is required to
make it. This is easily accounted for by the difference of the condi-
tions ; for no ordinary agitation can produce the same effect with the
curious movements of the stomach (§ 458); fresh gastric fluid is
poured out, as it is wanted, during the natural process of digestion ;
and the continual removal of the matter which has been already dis-
solved by its exit through the pylorus, is of course favourable to the
action of the' solvent upon the remainder. The quantity of food,
which a given amount of gastric fluid can dissolve, is limited ; pre-
cisely as in the case of the acidulous solution of pepsine. The
marked influence of temperature upon its action is shown by the fact,
that fresh gastric fluid has scarcely any influence on the matter sub-
mitted to it, when the bottle is exposed to cold air, instead of being
kept at a temperature of 100°. Hence the use of a large quantity of
cold water at meal-times, or of ice afterwards, must retard the diges-
tive process.

473. The pulpy substance, which is the product of the reducing
action of the gastric juice, is termed Chyme. Its consistence will of
course vary, in some degree, with the relative quantity of solids and
liquids ingested. In general it is grayish, semifluid, and homoge-
neous ; and possesses a slightly acid taste, but is otherwise insipid.
When the food has been of a rich oily character, the Chyme possesses
a creamy aspect ; but when it has contained a large proportion of fari-
naceous matter, it has rather the appearance of gruel. The state in
which the various alimentary principles exist in it, has not yet been
accurately determined ; the following, however, may be near the truth.
— The proteine-corapounds, whether derived from Animal or Vege-

278 SECRETION OF GASTRIC FLUID.

table food, are all reduced to the condition of Albumen ; a part of
which is dissolved^ whilst another portion is suspended in a very finely-
divided state. — Gelatin will be dissolved or not, according to its
previous condition ; if it exist in a tissue from which it cannot readily
be extracted, it will pass forth almost unchanged ; but when ingested
in a state of solution, it remains so ; and if it have been previously
prepared for solution by boiling, its solution is completed in the sto-
raach. — The Gummy matters of Vegetables are dissolved, when they
exist in a soluble form ; as in the case of pure gum, pectine, and dex-
trine or starch-gum. The degree in which Starch, when its vesicles
have not been ruptured by heat, is affected by the gastric fluid, seems
to differ in different animals ; the Ruminants and Granivorous Birds
apparently possessing the power of crushing or dissolving the enve-
lops of the starch-globules, whilst they pass through the alimentary
canal of other Herbivora unchanged, and may be detected entire in their
excrements. — Sugar is unquestionably taken up in solution, as such,
in a healthy condition of the system ; but it may undergo a previous
change in the stomach, in disordered states of the digestive process. —
Oily matters, whether of Animal or'Vegetable origin, are reduced to
the condition of an emulsion ; being very finely divided, and their
particles diffused through the chyme. — Most other substances, as
resins, woody fibre, horny matter, yellow fibrous tissue, &c., pass
unchanged from the stomach, and undergo no subsequent alteration
in the intestinal canal ; so that they are discharged among the feces
as completely useless.

474. We have now to notice the conditions, under which the Gas-
tric fluid is secreted ; the knowledge of which is of great practical
importance. We have seen that it is not poured forth, except when
food is introduced into the stomach, or when its walls are irritated in
some other mode ; and there is reason to believe, that it is not pre-
viously secreted and stored up in the follicles, but that the act of secre-
tion itself is due to the stimulus applied to the mucous membrane.
The quantity of the fluid then poured into the stomach, however, is
not regulated by the amount of food ingested, so much as by the
wants of the system ; and as only a definite quantity of food can be
acted on by a given amount of gastric juice, any superfluity remains
undissolved for some time, — either continuing in the stomach until a
fresh supply of the solvent is secreted, or passing into the intestinal
canal in a crude state, and becoming a source of irritation, pain, and
disease. The use of a small quantity of salt, pepper, mustard, or
other stimulating substances, appears to produce a gently stimulating
effect upon the mucous membrane, and by causing an increased. afflux
of blood, to augment the quantity of the gastric fluid poured forth.
Any excess of these or other irritants, however, produces a disordered
condition of the mucous membrane, which is very unfavourable to the
digestive process. It becomes red and dry, with an insufficient secre-
tion of mucus; the epithelial lining is abraded, so that the mucous
-coat is left entirely bare ; and irregular circumscribed patches of a

PRODUCTION OF CHYME— ADMIXTURE OF BILE. 279

deeper hue, sometimes with small aphthous crusts, present them-
selves here and there on the walls of the stomach. Similar results
follow excess in eating. When these changes are inconsiderable, the
appetite is not much impaired, the tongue does not indicate disorder,
and the digestive process may be performed ; but if they proceed
further, dryness of the mouth, thirst, accelerated pulse, foulness of the
tongue, and other symptoms of febrile irritation, manifest themselves ;
and no gastric secretion can then be excited by the stimulus of food.
Similar results may follow the excitement of the emotions ; and those
of a depressing nature seem especially to produce a pale flaccid con-
dition of the mucous membrane, which is equally unfavourable to the
due secretion of gastric fluid.

475. That the amount of the secretion is ordinarily proportioned to
the wants of the system, — that the introduction of any superfluous
aliment into the stomach is not only useless but injurious, as giving
rise to irritation, — that incipient disorder of the stomach may occur,
rendering it less fit than usual for the discharge of its important duties,
without manifesting itself by the condition of the tongue, — that when
the tongue does indicate disorder of the stomach, such disorder is
usually considerable, — and that every particle of food ingested, in
such states as prevent the secretion of gastric fluid, is a source of fresh
irritation, — are truths which cannot be too constantly kept in mind.
There can be no doubt that the habit of taking more food than the
system requires, is a very prevalent one ; and that it is persevered in
because no evil result seems to follow. But when it is borne in mind
that this habit must keep the stomach in a state of continual irritation,
however slight, it can scarcely be doubted that the foundation is thus
laid for future disorder, of a more serious kind. Two circumstances
especially tend to maintain this practice in adults, independently of
the mere disposition to gratify the palate. One is the habit of eating
the same amount of food, as during the period of growth, when more
was required by the system. The other is the custom of eating too
fast ; and this is injurious, — both by preventing sufficient mastication,
and thus throwing on the stomach more than its proper duty, — and
also by causing an over-supply of food to be ingested, before there is
time for the feeling of satisfaction to replace that of hunger (§ 486).

476. The Chyme, upon quitting the stomach, passes into the duo-
denum ; where it is mingled with the biliary and pancreatic secretions.
The secretion of Bile is evidently a process of the highest importance
in the economy ; as we may judge alike from the size of the liver and
the supply of blood it receives, and from the rapidly fatal effects of
its suspension. Yet the chemical nature of the secretion has not yet
been satisfactorily determined; and the destination of the fluid is still
a matter of doubt. That a large part of it is purely excrementitious,
and is poured into the intestinal tube for the purpose of being carried
out of the body, can scarcely be questioned ; but there is strong evi-
dence, that a part of it is destined to be absorbed again, after per-
fo rming some action of importance upon the contents of the alimentary

280 SECRETION OF BILE.

canal. There is a probability that a part of its function consists in
rendering the fatty matter of the aliment more soluble ; the nature of
the secretion being such, as to give it in some degree the action of
a soap. When fresh bile is mingled with newly-formed chyme, in
a glass vessel, the mixture separates into three distinct parts ; — a
reddish-brown sediment at the bottom, — a whey-coloured fluid in
the centre, — and a creamy pellicle at the top. The central and
upper strata probably constitute the portion which is destined for
absorption; whilst the sediment, partly consisting of the unreducible
portion of the food, and partly of the biliary matter itself, is evidently
excrementitious.

477. The composition of the Bile, and the structure of the organ
which elaborates it, will be more fitly considered when the Excre-
tions in general are treated of (Chap. IX.) ; at present we have only
to consider its relation to the digestive process. In all but the very
lowest animals, we find traces of a bile-secreting apparatus; and this
is almost constantly situated in the immediate neighbourhood of the
stomach. In many cases, the secretion is poured directly into the
cavity of that organ ; but in most, it is conveyed (as in Man) into the
intestinal tube near its commencement. There are few instances in
which the bile-ducts discharge themselves into the intestine low down,
and still fewer in which they terminate near its outlet ; and in these
last, they appear also to discharge the functions of urinary organs.
Hence it seems clear, from the disposition of the biliary apparatus,
that it has a purpose to serve in connection with the digestive func-
tion, and is not destined solely for the elaboration of a product which
is to be cast out of the body; since, if the latter were the case, that
product would be carried out immediately, like the urinary excretion,
and would not be discharged into the alimentary canal high up. — This
conclusion is confirmed by experiment ; for it has been shown by the
recent experiment of Schwann, that, if the bile-duct be divided, and
be made to discharge its contents externally through a fistulous ori-
fice in the walls of the abdomen, instead of into the intestinal canal,
those animals, which survive the immediate effects of the operation,
subsequently die from inanition, almost as soon as if they had been
entirely deprived of food. — The observation of disease in the human
subject leads to similar conclusions ; for, when the biliary secretion
is deficient, or its flow into the intestine is obstructed, the digestive
processes are evidently disordered ; the peristaltic action of the bowels
is not duly performed ; the feces are white and clayey ; and there is
an obvious insufficiency in the supply of nutriment prepared for the
absorbent vessels.

478. On the other hand, that one great object of the secretion is to
withdraw from the blood certain products of the decomposition of the
tissues, w^hich would otherwise accumulate in it, and would be dele-
terious to its character, is shown by evidence yet more decisive. We
find that the action of the Liver is constant^ and not occasional, like
that of the Salivary and Gastric glands ; and that, if anything inter-

SECRETION OF BILE. 281

fere with the secreting process, and thereby cause the accumulation
of the elements of the bile in the blood, the effects of their presence
are immediately manifested in the disorder of other functions, espe-
cially those of the nervous system (§ 399) ; and the continued suspen-
sion of the function leads to a fatal result, unless the elements of the
bile are drawn off' (as sometimes happens) by the urinary organs.
When the secreting action of the liver has once been performed, an
obstruction to the discharge of the bile into the intestine does not seem
to be so immediately injurious. The fluid accumulates, and distends
the bile-ducts and the gall-bladder ; and when they are completely
filled, part of it is re-absorbed into the blood, apparently in a changed
condition, since it does not then produce the same injurious effects
as result from the accumulation of the same materials, previously to
the action of the Liver upon them. The colouring-matter seems to
be very readily taken back into the circulating system; and is depo-
sited by it in almost every tissue of the body.

479. Although the secreting action of the Liver is constant, yet
the discharge of bile into the intestine is certainly favoured by the
presence of chyme in the latter. The purpose of the gall-bladder is
obviously to permit the accumulation of bile, when it is not wanted
in the intestine ; and we find it most constantly present in those tribes
of animals, which live upon animal food, and which therefore take
their aliment at intervals ; whilst it is more frequently absent in those
herbivorous animals, in which the digestive process is almost con-
stantly going on. The middle coat of the bile-ducts is clearly mus-
cular, and has a peristahic action like that of the intestinal canal ; this
action may be excited by galvanism, or by irritation of the branches
of the Sympathetic nerve, by which it is supplied. The mucous coat
of the ductus choledochus is disposed in valvular folds, in such a man-
ner as to prevent the reflux of the bile or of the contents of the intes-
tine ; and a still further security is afforded by the valvular covering
to the orifice of the duct, which is furnished by the mucous covering
of the intestine itself. The flow of bile into the intestine, when its
presence is needed there, is commonly imputed to the pressure of the
distended Duodenum against the gall-bladder ; but it is probable that
the contractility of the muscular coat of the duct itself, which may be
excited either through the sympathetic nerve, or by irritation at the
orifice of the duct (as in the case of the Salivary glands) is the real
cause of the discharge of the fluid. It is an interesting fact, which
proves how much the passage of the Bile into the Intestine is depend-
ent upon the presence of aliment in the latter, that the gall-bladder is
almost invariably found turgid in persons who have died of starvation;
the secretion having accumulated, through the want of demand for it,
although there was no obstacle to its exit.

480. The Pancreatic secretion appears to have nearly the same
qualities as Saliva ; the proportion of solid matter, however, being
usually greater. Of its uses in the digestive process, nothing definite
can be stated.

282 SENSE OF HUNGER.

481. During the passage of the contents of the Intestine, now aug-
mented by the biliary secretion, along the canal, the nutritious portion
is gradually withdrawn by the absorbent vessels on its walls ; and the
excrementitious matter alone remains. This is increased in amount
by the products of the secretion of the various glandulse, with which
the mucous lining of the intestines is studded. As their function,
however, is obviously to get rid of decomposing matter from the sys-
tem, rather than to contribute in any way to the preparation of the
nutritive materials, it will be more properly considered hereafter
(Chap. XI). Many of the lower animals are furnished, at the part
where the small intestine enters the large, with a ccBcum, resembling
that which in Man is termed the vermiform appendage of the csecum,
but greatly exceeding it in size. Sometimes we find two caeca in-
stead of one ; and these are much prolonged, so as to form tubes of
considerable length. It has been ascertained that, in herbivorous
animals, a distinctly acid secretion is formed by the caecum, during
the digestive process ; and there is reason to believe, that the food
there undergoes a second process, analogous to that to which it has
been submitted in the stomach, and fitted to extract from it any un-
dissolved alimentary matter it may still contain. There is no reason
to believe, however, that any such process takes place in Man, whose
real caecum is rudimentary, — the part of the intestine which has re-
ceived the name, being merely the dilated commencement of the
colon. The act of defecation, by which the excrementitious matter
is discharged, has been already noticed (§ 462); the Absorption of
nutritive matter will be treated of in the succeeding Chapter.

5. Of Hunger, Satiety, and Thirst.

482. The want of solid aliment is indicated by the sensation of
Hunger ; and the deficiency of fluid by that of Thirst. On the other
hand, the presence of a sufficiency of food or liquid in the stomach is
indicated by the sense of Satiety. These sensations are intended as
our guides, in regard to the amount of aliment we take in. What is
the real seat of these sensations, and on what conditions do they
depend ?

483. The sense of Hunger is referred to the stomach, and seems
immediately to depend upon a certain condition of that organ ; but
what that condition is, has not yet been precisely ascertained. It is
not produced by mere emptiness of the stomach, as some have sup-
posed ; for, if the previous meal have been sufficient, the food passes
entirely from the cavity of the stomach, before a renewal of the sensa-
tion is felt. It cannot be due to the action of the gastric fluid upon
the coats of the stomach themselves ; because this fluid is not poured
into the stomach, except when the production of it is stimulated by
the irritation of the secreting follicles. It has been attributed to dis-
tension of the gastric follicles by the secreted fluid ; but there is no
evidence that the fluid is secreted before it is wanted ; and, moreover,

SENSE OF HUNGER AND SATIETY. 283

it is well known that mental emotion can dissipate in a moment the
keenest appetite, and it is difficult to imagine how this can occasion
the emptying of the follicles. Perhaps the most satisfactory view is
that, which attributes the sense of hunger to a determination of blood
to the stomach, preparing it for the secretion of gastric fluid ; since
this is quite adequate to account for the impression made upon the
nerves; and it accords with what has just been stated of the influence
of mental emotions, since we know that these have a powerful effect
upon the circulation of blood in the minute vessels (§ 603).

484. Although the sense of Hunger is immediately dependent, in
great part at least, upon the condition of the stomach, yet it is also
indicative of the condition of the general system ; being extremely
strong, when the body has undergone an unusual waste without a due
supply of food, even though the stomach be in a state of distension ;
whilst it is not experienced, if, through the general inactivity of the
system, the last supply has not been exhausted, even though the sto-
mach has been long empty. It is well known, that when food is defi-
cient, the attempt to allay the pangs of hunger by filling the stomach
with non-nutritious substances, is only temporarily successful; the
feeling soon returning wath increased violence, though it has received a
temporary check. The reason for this is obviously, that the general
system has received no satisfaction, although the stomach has been
caused to secrete gastric fluid by the contact of solid matter with its
walls, so that the state on which hunger immediately depends, has
been for a time relieved. This state is soon renewed, unless the solid
matter introduced into the stomach be of an alimentary character, and
be dissolved and carried into the system.

485. When the food is nutritious in its character, but of small bulk,
experience has shown the advantage of mixing it with non-nutritious
substances, in order to give it bulk and solidity; for if this be not
done, it does not exert its due stimulating influence upon the stomach ;
the gastric juice is not poured forth in proper quantity ; and the result
is, that neither is the sense of hunger relieved, nor are the wants of
the body satisfied. Thus the Kamschatdales are in the habit of
mixing earth or saw-dust with the train-oil, on which alone they are
frequently reduced to live. The Veddahs or wild hunters of Ceylon,
on the same principle, mingle the pounded fibres of soft and decayed
wood with the honey on which they feed when meat is not to be had ;
and on one of them being asked the reason of the practice, he replied,
" I cannot tell you, but I know that the belly must be filled." It has
been found that soups and fluid diet are not more readily converted
into chyme than solid aliment, and are not alone fit for the support of
the body in health ; and it is often to be observed, in disordered states
of the stomach, that it can retain a small quantity of easily-digested
solid food, when a thin broth would be rejected.

486. The sense of Satiety is the opposite of Hunger ; and like it,
depends on two sets of conditions, — the state of the stomach, and that
of the general system. It is produced in the first instance by the

284 HUNGER, SATIETY, AND THIRST.

ingestion of solid matter into the stomach, which gives rise to the
feeling of fullness ; but this is only a part of the sensation which ought
to be experienced ; and it is only when the act of digestion is being
duly performed, and nutritive matter is being absorbed into the ves-
sels, that the peculiar feeling of satisfaction is excited, which indicates
that the wants of the system at large are being supplied. — It has been
very justly remarked by Dr. Beaumont, that the cessation of the de-
mand set up by the system, rather than the positive feeling of satiety,
should be the guide in regulating the quantity of food taken into the
stomach. The sense of satiety is beyond the point of healthful indulg-
ence ; and is Nature's earliest indication of an abuse and overburdening
of her powers to replenish the system. The proper intimation is the
pleasurable sensation which is experienced, when the cravings of the
appetite are first allayed ; since, if the stomach be sufficiently distended
with wholesome food, for this to be the case, it is next to certain that
the digestion of that food will supply what is required for the nutrition
of the body. It is only when the substance with which the stomach
is distended, is not of a digestible character, that the feelings excited
by the .state of that organ are anything but a correct index of the
wants of the system.

487. The Par Vagum is evidently the nerve, which conveys to the
sensorium the impression of the state of the stomachy and which is
therefore the immediate excitor of the sensation of hunger, or of the
feeling of satiety. But it is evident from experiments upon animals,
that it is not the only source, through which they are incited to take
food, and are informed when they have ingested enough ; and it is
probable that the Sympathetic nerve is the channel, through which
the wants of the system are made known, and through which, in
particular, the feeling of general exhaustion is excited, that is expe-
rienced when there has been an unusual waste, or when the proper
supply has been too long withheld.

488. The conditions of the sense of Thirst are very analogous to
those of hunger; that is, it indicates the deficiency of fluid in the
body at large ; but the immediate seat of the feeling is a part of the
alimentary canal, — not the stomach, however, but the fauces. It is
relieved by the introduction of fluid into the circulating system,
through any channel ; whilst the mere contact of fluids with the sur-
face to which the sensation is referred, produces only a teniporary
effect, unless absorption take place. If liquids be introduced into the
stomach by an oesophagus-tube, they are just as effectual in allaying
thirst, as if they w^ere swallowed in the ordinary manner ; and the
same result follows the injection of fluid into the veins, (as was most
remarkably the case when this method of treatment was practised in
the Asiatic Cholera,) or the absorption of fluid through the skin or the
lower part of the alimentary canal. The deficiency of fluid in the
body may arise, — and Thirst may consequently be induced, — either
by an unusually small supply of fluid, or by excessive loss of the fluids
of the body, as by perspiration, diarrhoea, &c. But it may also be

ABSORPTION FROM THE DIGESTIVE CAVITY. 285

occasioned by the impression made by particular kinds of food or
drink upon the alimentary canal ; thus salted or highly-spiced meat,
fermented liquors when too little diluted, and other similar irritating
agents, excite thirst ; the purpose of which sensation is evidently to
cause the ingestion of fluid, by which these substances may be diluted,
and their irritating action prevented.

I

CHAPTER V.

ABSORPTION AND SANGUIFICATION.

1. Absorption from the Digestive Cavity.

489. So long as the Alimentary matter is contained in the digestive
cavity, it is as far from being conducive to the nutrition of the sys-
tem, as if it were in contact with the external surface. It is only
when absorbed into the vessels, and carried by the circulating current
into the remote portions of the body, that it really becomes useful in
maintaining the vigour of the system, by replacing that which has
decayed, and by affording the materials for the various organic pro-
cesses which are continually going on. Among the Invertebrated
animals, we find the reception of alimentary matter into the circula-
ting system to be entirely accomplished through the medium of the
veinSy which are distributed upon the walls of the digestive cavity.
We not unfrequently observe, that the intestinal tube is completely
enclosed within a large venous sinus, so that its whole external sur-
face is bathed with blood ; and into this sinus, the alimentary mate-
rials would appear to transude, through the walls of the intestinal
canal, to become mingled with the blood, and to be conveyed with
its current into the remote portions of the body. Among the Verte-
brata, we find an additional set of vessels, interposed between the
w^alls of the intestine and the sanguiferous system, for the purpose,
as it would seem, of taking up that portion of the nutritive matter
which is not in a state of perfect solution, and of preparing it for
being introduced into the current of the blood. These vessels are the
ladeals or absorbents. They are very copiously distributed upon the
walls of the small intestine, commencing near the entrance of the
biliary and pancreatic ducts; the walls of the large intestine are less
abundantly supplied with them, and they are not to be met with at all
on the walls of the stomach.

490. Nevertheless it is quite certain, that substances may pass into
the current of the circulation, which have been prevented from pass-
ing further than the stomach ; thus, if a solution of Epsom-salts be
introduced into the stomach of an animal, and its passage into the

286 ABSORPTION BY ENDOSMOSE.

intestine be prevented by a ligature around the pylorus, its purgative
action will be exerted nearly as soon, as if the communication between
the stomach and intestines had been left quite free ; or if a solution
of prussiate of potash be introduced into the stomach under similar
circumstances, the presence of that salt in the blood may be speedily
demonstrated by chemical tests.

491. This passage of substances in a state of perfect solution, from
the stomach into the blood-vessels, is probably due to the operation
of that peculiar modification of Capillary Attraction, which is called
Endosmose. When two fluids differing in density are separated by a
thin animal or vegetable membrane, there is a tendency to mutual
admixture through the pores of the membrane; but the less dense
fluid will transude with much greater facility than the more dense ;
and consequently there will be a considerable increase on the side of
the denser fluid ; whilst very little of this, in comparison, will have
passed towards the less dense. When one of the fluids is contained
in a sac or cavity, the flow of the other towards it is termed Endos-
ttiose, or flow-inwards ; whilst the contrary current is termed Exos-
mose or flow-outwards. Thus if the caecum of a fowl, filled with
syrup or gum-water, be tied to the end of a tube, and be immersed
in pure water, the latter will penetrate the caecum by Endosmose, and
will so increase the volume of its contents, as to cause the fluid to
rise to a considerable height in the attached tube. On the other hand,
a small proportion of the gum or syrup will find its way into the sur-
rounding fluid by Exosmose. But if the csecum were filled with
water, and were immersed in a solution of gum or sugar, it would soon
be nearly emptied, — the Exosmose being much stronger than the En-
dosmose. It is in this manner that we may cause the flattened corpus-
cles of the blood to be distended into spheres, by treating them with
water; or may empty them almost completely, by immersing them in
syrup (§ 216); since their contents are more dense than the surround-
ing fluid in the first case, so that they will be augmented by Endos-
mose ; whilst they are less dense in the second, so as to be diminished
by Exosmose.

492. Now it seems to be in this manner, that substances contained
in the cavity of the stomach, and perfectly dissolved by its fluids, are
received into the blood-vessels; for as the blood is the fluid of greater
density, it will have a tendency to draw towards it, by Endosmose,
the saline and other matters, which are in a state of perfect solution in
the stomach. The mucous membrane, which forms the inner wall of
that organ, is most copiously supplied with blood-vessels ; partly,
indeed, that they may afford the materials of the gastric secretion ; but
partly, also, that they may take up the substances, which are capable
of entering the circulating current by this direct channel. That this
act of absorption is principally effected by the veins rather than by
the arteries, appears from several considerations. The walls of the
former are much thinner than those of the latter. Moreover, the for-
mer are usually distributed nearer to the surface ; whilst the latter are

ABSORPTION OF SOLUBLE MATTERS INTO THE VEINS. 287

more deeply-seated. And the direction of the passage of the blood
in the former is favourable to the act of absorption, whilst in the latter
it is the reverse ; for the blood in the arteries is passing from large
trunks, through which it flows with facility, into the innumerable sub-
divisions and ramifications of the capillary system, in which the resist-
ance to its flow is very much increased ; whilst in the veins, the
numerous streams flowing through the capillaries are uniting and con-
verging into main trunks of greatly-increased capacity, so that the
resistance is greatly diminished ; and it is easily shown on Physical
principles, that the former condition presents a direct obstacle to
absorption, whilst the latter as directly favours it. For if a current
of fluid be made to pass through a horizontal tube, which undergoes
an enlargement at one part of its course, so that the fluid passes from
the smaller to the larger portion, and if a small tube be made to open
into the enlarged part, and to dip down vertically into a basin below,
the fluid of that basin will be caused to rise in the small tube, so as
to be drawn into the current that is flowing through the horizontal
pipe, — and this with a force proportional to the amount of its enlarge-
ment, and to the rapidity of the current that is flowing through it.

493. Although it is difficult to speak with certainty on the point,
yet there appears a strong probability that, both in the stomach and
intestinal tube, the absorption of nutritive matters in a state of per-
fect solution^' — such as gum, sugar, pectine, gelatin, and soluble
albumen, — is thus accomplished through
the medium of the veins ; which also Fig. 77.
take up the chief supply of water that is
required by the system. It is difficult
else to see the purpose of the extraordir
nary vascularity of the mucous mem-
brane, and in particular of those fila-
ments or narrow folds, termed villi,
which so thickly cover its surface. Each
of these villi is furnished with a plexus ^. ., . . ^

« . , , , 1 , ^ 1 -1 .1 Distribution of Capillaries in the

ot minute blood-vessels, 01 which the viiu of the intestine.
larger branches may even be seen with

the naked eye, when they are distended with blood or with a coloured
injection. By these villi, the vascular surface of the mucous mem-
brane is enormously extended. In Man, they are commonly cylin-
drical or nearly so, and are from about a quarter of a line to a line
and a half in length ; but in many of the lower animals they are
spread out into broader laminae at the base, and are connected
together so as to form ridges or folds. — It appears from the experi-
ments of MM. Tiedemann and Gmelin, that when various substances
were mingled with the food, which, by their colour, odour, or chemi-
cal properties, might be easily detected, — such as gamboge, madder,
rhubarb, camphor, musk, assafetida, and saline compounds, — they
were seldom found in the chyle, though many of them were detected
in the blood and in the urine. The colouring matter appeared to be

288 ABSORPTION INTO THE LACTEALS.

seldom absorbed at all ; the odorous substances were generally de-
tected in the venous blood and in the urine, but not in the chyle;
whilst, of the saline substances, many were found in the blood and
in the urine, and only a very few in the chyle.

494. Every one of the intestinal Villi, however, also contains the
commencement of a proper absorbent vessel ; and this system of ves-
sels has received the name oi lacteal^ on account of the milky aspect
of the fluid which is found within it. The accompanying figure
represents the appearance offered by the incipient lacteals in a villus
of the jejunum of a young man, who had been hung soon after taking

a full meal of farinaceous food. The trunk that
^2^^^^ issues from the villus is formed by the conflu-
ence of several smaller branches, whose origin
it is difficult to trace; but it is probable that
they form loops by anastomosis with each other,
so that there is no proper free extremity in any
case. It is quite certain that the lacteals never
open by free orifices upon the surface of the
intestine, as was formerly imagined. From the
researches of Mr. Goodsir, already referred to,
it appears that these loops are imbedded in a
One ofthe intestinal villi, mass of cclls, w^hich are the real agents in the

•with the commencement of i .• r xi. i. * i xi i. i i* i ^

a lacteal. selcctiou ot the materials that are destined to

be conveyed into the lacteals; and that the
growth of these cells is the first stage of the process, by which the
nutritive matters that are in a state of very fine division^ but not in
perfect solution^ are received into the system (§ 241). When these
cells have completed their ofldce, and have passed through the term
of their lives, they yield their contents to the absorbent vessels, either
by bursting or by deliquescence; and thus the substances whicl^i they
have selected and combined by their own processes of growth, are
delivered to the current in which they are to undergo further trans-
formations, and to be made subservient to the nutrition of the general
system.

495. It is particularly important to keep in view the difference
between the two modes by which alimentary substances are intro-
duced into the system, when we are treating those disordered states
in which the digestive process is imperfectly performed, or altogether
suspended. There can be little doubt, that the immediate cause of
death, in many diseases of exhaustion, is the want of power to main-
tain the heat of the body ; the stomach not being able to dissolve
food, and the functions of the lacteals being altogether suspended,
by the non-development of the absorbing cells, so that the inanition
is as complete as if food were altogether withheld. Now under such
circumstances, it becomes a matter of greatest importance to present
a supply of combustible matter, in such a form that it may be intro-
duced into the circulating system by simple Endosmose ; and the
value which experience has assigned to weak broths and thin fari-

ABSORPTION OF ALCOHOL, ETC.— MESENTERIC GLANDS. 289

naceoiis solutions, and still more, to diluted alcoholic drinks, fre-
quently repeated, under such circumstances, seems to depend in
great part upon the facility with which they may be thus absorbed.
The good effects of alcohol, cautiously administered, are no doubt
owing in part to its specific influence upon the nervous system ; but
that they are also due to its heat-producing power, appears from
the results of the administration of frequently-repeated doses, in
states of utter exhaustion, — the temperature of the body being kept
up so long as they are continued, and falling when they are inter-
mitted. As the alcohol is thus burned off", nearly as fast as it is
introduced, it never accumulates in sufficient quantity to produce its
usual violently-stimulating effects upon the nervous system.

2. Passage of the Chyle along the Ladeals, and its admixture with the
Lymph collected from the general System.

496. The Lacteal vessels, which commence on the surface of the
intestines, run together on their walls, and form larger trunks, which
converge and unite with each other in the mesentery; and the main
trunks thus formed then enter certain bodies, which are commonly
known as the ** mesenteric glands." Their structure, however, does
not seem to correspond with that of the proper glands ; as they are

Fisr. 79.

Fig. 80.

Diagram of a lymphatic gland, showing the in-
tra-glandular network, and the transition from
the scale-like epithelia of the extra-glandular
lymphatics, to the nucleated cells of the intra-
glandular.

Portion of intra-glandular lymphatic, showing
along the lower edge the thickness of the germi-
nal membrane, and, upon it, the thick layer of
glandular epithelial cells.

simply composed of lacteal trunks, convoluted into knots, and dilated
into larger cavities, amongst which blood-vessels are minutely dis-
tributed. These blood-vessels have no direct communication with
the interior of the lacteals; but are separated from them by the mem-
branous walls of both sets of tubes. The epithelium, which lines the
absorbent vessel, undergoes a marked change where the vessel enters
the gland, and becomes more like that of the proper glandular fol-
licles in its character. Instead of being flat and scale-like, and form-
ing a single layer in close apposition with the basement-membrane,
as it does in the lacteal tubes before they enter the gland and after
they have emerged from it, w^e find it composed, within the gland,
of numerous layers of spherical nucleated cells (Figs. 79 and 80);
of which the superficial ones are easily detached, and appear to be
19

290

TERMINATION OF LACTEALS IN THORACIC DUCT.

Fig. 61.

identical with the cells that are found floating in the chyle. TJie
purpose of these cells will be presently inquired into.

497. After emerging from
the mesenteric glands, the
lacteal trunks converge, with
occasional union, until they
discharge their contents into
the receptaculum chyli, which
is situated at the front of the
body of the second lumbar
vertebra. Into the same cav-
ity are poured the contents
of a part of the other division
of the Absorbent system;
which is distributed through
the body in general, and
which, from the transparency
of the fluid or lymph it con-
tains, is termed the lymphatic
system. From the recepta-
culum chyli arises the thora-
cic duct; which passes up-
wards in front of the spine,
receiving other lymphatic
trunks in its course, to ter-
minate at the junction of the
left subclavian and jugular
veins; where it delivers its
contents into the sanguiferous
system. A smaller duct re-
ceives some of the lymphatics
of the right side, and there
terminates at a corresponding
part of the venous system ;
but it does not receive any
of the contents of the lac-
teals.

498. The lymphatic sys-
tem is evidently allied very
closely to the lacteal, in
its general purposes ; and
makes its first appearance
in the same class of ani-
mals, namely, in Fishes.

The course and termination of the thoracic duct. 1.
The arch of the aorta. 2. The thoracic aorta. 3. The
abdominal aorta; showing its principal branches di-
vided near their origin. 4. The arteria innominata, di-
viding into the right carotid and right subclavian arteries.
5. Tlie left carotid. 6. The left subclavian. 7. The su-
perior cava, formed by the union of, 8, the two vinae in-
nominatae; and these by the junction, 9, of the internal
jugular and subclavian vein at each side. 10. The greater
vena azygos 11. The termination of the lesser in the
greater vena azygos. 12. The receptaculum chyli ; seve-
ral lymphatic trunks are seen opening into it. 13. The tho-
racic duct, dividing opposite the middle of the dorsal ver-
tebrae into two branches, which soon reunite; the course
of the duct behind the arch of the aorta and left subclavian
artery is shown by a dotted line. 14. The duct making its
turn at the root of the neck, and receiving several lym-
phatic trunks previously to terminating in the posterior
aspect of the junction of the internal jugular and subcla-
vian vein. 15. The termination of the trunk of the ductus
lymphaticus dexter.

The vessels of which it is
composed are distributed through most of the softer tissues of the
body, and are particularly abundant in the skin. They have never
been found to commence by closed or open extremities ; but seem to

LACTEAL AND LYMPHATIC SYSTEMS. 291

form a network, from which the trunks arise. In their course they
pass through glands, disposed in different parts of the body, which
exactly resemble in structure those which are found upon the lacteals
in the mesentery. And they at last terminate, as already shown, in
the same general receptacle with the lacteals. Hence it cannot be
reasonably doubted, that the fluid which they absorb from the various
tissues of the body, is destined to become again subservient to nutri-
tion ; being poured back into the current of the blood, along with the
new materials, which are now for the first time being introduced into
it. That the special Absorbent apparatus of Vertebrated animals has
for part of its functions to effect a change in the materials absorbed,
and thus to aid in fitting them for introduction into the blood, seems
apparent from the facts of Comparative Anatomy ; which show that,
the more distinct the blood is from the chyle and lymph, the more
marked is the provision for delaying the latter in the absorbent sys-
tem, and for subjecting it to preliminary change.

499. The course of the lymphatic and lacteal vessels in Fishes is
short and simple ; they are not furnished with glands ; and they pour
their contents into the blood-vessels at several different parts of the
body. In this class the blood contains fewer red corpuscles, and its
coagulating power is feebler than in any other Vertebrata. And in
the lowest tribes, in which the Vertebrated character is almost entirely
wanting, and in which the blood is almost pale, no special absorbent
system has yet been discovered. In Reptiles, the length of the ab-
sorbent vessels is remarkably increased by their doublings and convo-
lutions ; so that the system appears to be more highly developed than
in either of the warm-blooded classes. But this superiority is not
real ; for there is yet no trace of the glands, which concentrate, as it
were, the assimilating power of a long series of vessels. Moreover,
we often find the lymphatics of this class furnished with pulsating dila-
tations, or lymphatic hearts ; which have for their office to propel the
lymph into the venous system. In the Frog there are two pairs of
these; one situated just beneath the skin (through which its pul-
sations are readily seen in the living animal), immediately behind the
hip-joint ; the other pair being more deeply seated at the upper part
of the chest. The former receive the lymph of the posterior part of
the body, and pour it into the veins proceeding from the same part ;
the latter collect that which is transmitted from the anterior part of
the body and head, and empty their contents into the jugular vein.
Their pulsations are totally independent of the action of the heart,
and of the respiratory movements ; since they continue after the
removal of the former, and for an hour or two subsequently to the
death and complete dismemberment of the animal. They usually take
place at the rate of about sixty in the minute ; but they are by no
means regular, and are not synchronous on the two sides.

500. In Birds, we find the absorbent system existing in a more
perfect form ; its diffused plexuses and convolutions being replaced
by glands ; in which the contained fluid is brought into closer proxi-

^95i ABSORPTION BY THE LYMPHATICS.

mity with the blood ; and in which it is subjected to the influence of
assimilating cells. These, however, are not very numerous ; being
principally found on the lymphatics of the upper extremities. The
absorbents, in this class, terminate principally by two thoracic ducts,
one on each side, which enter the jugular veins by several orifices.
There are, however, two other entrances, as in Reptiles, into the
veins of the lower extremity ; and these are connected with two large
dilatations of the lymphatics, which are evidently analogous to the
lymphatic hearts of Reptiles, but which have little or no power of
spontaneous contraction. — In Mammalia, the absorbent system pre-
sents itself in its most developed and concentrated state. The vessels
possess firmer walls, and are more copiously provided with valves,
than in the classes beneath; and the glands are much more numerous,
particularly upon the vessels that receive or imbibe substances from
without, — as those of the digestive cavity, the skin, and the lungs.
The terminations of the absorbents in the veins are usually restricted,
as in Man, to the single point of entrance of the thoracic duct on
either side ; but they are sometimes more numerous ; and certain
variations in the arrangement of the thoracic ducts, which occasion-
ally present themselves as irregularities in Man, are the ordinary con-
ditions of these parts in some of the lower Mammalia.

501. With regard to the source of the matters absorbed by the
lymphatics, it is difficult to speak with certainty. We shall presently
see that their contents bear a close resemblance to the fluid element
of the blood, or " liquor sanguinis," in a state of dilution ; and it is
very probable that they partly consist of the residual fluid, which,
having escaped from the blood-vessels into the tissues, has furnished
the latter with the materials of their nutrition, and is now to be re-
turned to the former. But they may include, also, those particles of
the solid frame-work, which have lost their vital powers, and which
are not fit therefore to be retained as components of the living system,
but which have not undergone a degree of decay which prevents
them from serving, like matter derived from the dead bodies of other
animals, as a material for reconstruction, when it has been again sub-
jected to the organizing process.

502. It was formerly supposed (and the doctrine was particularly
inculcated by the celebrated John Hunter), that the office of the Lym-
phatic system is to take up and remove all the effete matter, that is
to be cast out of the body, being no longer fit for its nutrition. But
for such a supposition there is no adequate foundation. It seems
absurd to imagine, that this effete matter would be mingled with the
newly-ingested aliment, and would be poured back with it into the
general current of the circulation, instead of being at once carried
out of the system. And the idea is directly negatived, as we shall
presently see, by the actual composition of the lymph drawn from
these vessels ; the solid matter of which consists, in great part at least,
of substances of a nutritive character. It is true that other substances
are occasionally found in the lymphatics; thus, when the gall-bladder

MOVEMENT OF FLUID IN ABSORBENTS. 293

and bile-ducts are over-distended with bile, in consequence of some
obstruction to its exit, the lymphatics of the liver are found to contain
a biliary fluid. In like manner, the lymphatics in the neighbourhood
of a large abscess have been found to contain pus. When the limb
of an animal, round the upper part of which a bandage is tied, is kept
for some hours in tepid milk, the lymphatics of the skin are found
distended with that fluid. And when saline solutions are applied to
the skin, they are usually detected more readily in the lymphatics,
than in the veins. But these facts only prove, that the lymphatics
very readily imbibe soluble substances with which they are in proxi-
mity; and this imbibition seems to take place on the same physical
principles, as the imbibition of soluble substances by the veins of the
intestinal canal.

503. The more ready absorption of such substances by the lympha-
tics, than by the veins, of the cutaneous surfaces, — contrary to what
obtains in the alimentary canal, — is easily accounted for, by the very
abundant distribution of the lymphatics in the skin, and the ready
access which fluids can obtain to their walls. In other tissues it is
different ; thus it appears that saline matters injected into the lungs
are detected much sooner in the serum of the blood than they are in
the lymph ; and make their appearance earlier in the left cavities of
the heart, to which they would be conveyed by the pulmonary vein,
than in the right, which they would reach through the thoracic duct
and descending cava. This is obviously due to the minute distribu-
tion of the blood-vessels upon the walls of the air-cells; which makes
them far more ready channels for the imbibition of fluid, than the
lymphatics could be. — In regard to the occasional absorption of pus
from the cavity of an abscess or of an open ulcer, by the lymphatics,
it is to be remarked that the absorbent vessels must themselves pro-
bably be laid open by ulceration ; since in no other way can we un-
derstand the entrance of globules, so large as those of pus, into their
interior.

504. In regard to the cause of the movement of the chyle and
lymph along the absorbent vessels, from their commencement to their
termination in the central receptacle, no very definite account can be
given. The middle coat of these vessels has a fibrous texture ; and
the fibres bear some resemblance to that of the non-striated muscle.
In the thoracic duct, this fibrous structure is more evident ; and dis-
tinct contractions have been excited in it, by irritating the sympathe-
tic trunks from which it receives its nerves, and the roots of the spinal
nerves with which those trunks are connected. Hence it seems pro-
bable, that there is a sort of peristaltic contraction of the walls of the
absorbents, analogous to that which takes place in the intestinal tube,
serving to drive their contents slowly onwards ; their reflux being
prevented by the valves, with which they are copiously furnished.
Moreover, it is probable that the general movements of the body may
concur with the contractile power of the absorbent vessels themselves,
to urge their contents onwards ; for almost every change in position

2^ STRUCTURE AND FUNCTIONS OF THE SPLEEN.

must occasion increased pressure on some portion of them, which will
propel the fluid contents in the sole direction permitted by the valves,
and thus give them an additional impulse towards the trunks, in which
they are collected for delivery into the blood-vessels.

3. Of the Spleen^ and other Glandular Appendages to the Lymphatic

System.

505. The structure and functions of the Spleen, and of certain
other organs allied to it in character, have been among the most
obscure subjects in Anatomy and Physiology; and they are far from
having been yet fully elucidated. There seems sufficient evidence,
however, for regarding them in the light of appendages to the Lym-
phatic system, and as concerned, like it, in the process of Sanguifica-
tion, or the preparation of Blood. Hence this appears to be the most
appropriate place, for such a brief notice of them, as the present state
of our knowledge admits.

506. The Spleen is certainly to be regarded as an organ of com-
pound structure, having at least two sets of functions to fulfil. It is
essentially composed of a fibrous membrane, which constitutes its
exterior envelop, and which sends prolongations in all directions
across its interior, so as to divide it into a number of minute cavities
or follicles of irregular form. These splenic follicles communicate
freely with each other, and with the splenic vein, and they are lined
by a continuation of the lining membrane of the latter. The partitions
between the follicles are formed, not only by these membranes, but
by the peculiar parenchyma of the Spleen ; and this seems to be made
up of reticulations of blood-vessels and lymphatics, with a large
quantity of minute globules or incipient cells, of about half the dia-
meter of blood-corpuscles, which lie in the meshes of the capillary
network, and which seem to be in intimate connection with the lym-
phatics. Lying in the midst of this parenchyma, there are found a
large number of bodies, about one-third of a line in diameter, which
are known as the Malpighian bodies of the Spleen. These resemble
lymphatic glands in miniature, being composed of convoluted masses
of blood-vessels and lymphatics, united by elastic tissue ; and the
lymph they contain is rendered somewhat milky by the large number
of the lymph-corpuscles that float in them, although the fluid of the
afferent lymphatics is quite clear; — so that the correspondence both
in structure and function seems to be exact.

507. The parenchymatous and the cellated structures do not seem to
bear any constant proportion to each other; thus the former prevails
most in Man, and the latter in the Herbivora. The walls of the fol-
licles are so elastic, that their cavities may be greatly distended with
a very moderate force, — the Spleen of the sheep, which weighs about
4 oz., being easily made to contain about 30 oz. of water. This pecu-
liar distensibility evidently points to the Spleen as a kind of reser-
voir, connected with the Portal circulation, for the purpose of reliev-

STRUCTURE AND FUNCTIONS OF THE SPLEEN. 295

ing the portal vessels from undue pressure or distension, under a great
variety of circumstances. The portal system is well known to be
destitute of valves, so that the splenic vein communicates freely with
the whole of it; and thus, if any obstruction exist to the flow of
blood through the liver, or any peculiar pressure elsewhere prevents
the mesenteric veins from dilating to, their full extent, the general cir-
culation is not disturbed, — the Spleen affording a kind of safety-valve.
That any cause of congestion of the Portal system peculiarly affects
the Spleen, has been proved by experiment ; for, after the portal vein
has been tied, the spleen of an animal that previously weighed only
2 oz., has been found to increase 20 oz. Further, in Asphyxia,
when the circulation of blood is checked in the Lungs, and when the
stagnation extends itself backwards to the right side of the heart, to
the vena cava, and thence to the portal system, the Spleen is often
found after death to be enormously distended with blood. And in
the cold stage of intermittent fever, in which a great quantity of blood
is driven from the surface towards the internal organs, the Spleen
receives a large portion of it, so that its increased size becomes quite
perceptible ; and in cases of confirmed Ague, the Spleen becomes
permanently enlarged, forming what is popularly known as the ** ague-
cake." — Again, the Spleen appears to serve as a reservoir, into which
superfluous blood may be carried, during the digestive process.
When the alimentary canal is distended with food, and a great afflux
of arterial blood takes place to the mucous membrane, the veins of
the portal system will be liable to increased pressure from without,
whilst their contents will be augmented by the quantity of fluid newly
absorbed from the alimentary canal. In this, as in the preceding
cases, the distensibility of the spleen makes it a kind of safety-valve,
by which undue distension of the portal system is relieved. It has
been ascertained that its maximum volume is attained about five hours
after a meal, when the process of chymiiication is at an end, and that
of absorption is taking place with activity ; and the increase is pro-
portional rather to the amount of the fluids ingested, than to that of
the solids.

508. But besides this safety-valve function, there can be little ques-
tion that the Spleen performs another, which corresponds with the
function of the lymphatic glands in general. The identity in struc-
ture between its Malpighian bodies, and the ordinary lymphatic glands,
is such as clearly points to this inference ; and it is confirmed by this
remarkable fact, which has been ascertained by recent experiments, —
that after the spleen has been extirpated, the lymphatic glands of the
neighbourhood increase in size, and cluster together as they enlarge,
so as to form an organ that at least equals the original spleen in volume.
This circumstance explains the reason of the almost invariable negative
result of the extirpation of the spleen; for although the operation has
been frequently practised, with the view of determining the functions
of the organ by the symptoms presented by the animals after its re-

29$. SUPRA-RENAL CAPSULES.

moval, no decided change in the ordinary course of their vital pheno-
mena has ever been observed, and the health, if at all disturbed for
a time, is afterwards completely regained. Now if the functions of
the Spleen, — putting aside the safety-valve action of its distensible'
cavities, — be the same with that of the lymphatic glands in general,
it is easy to^ understand how its loss may be at once compensated by
an increased action on their part, and how it may be permanently
replaced by an increased development of certain of those bodies. —
Thus, then, we may fairly regard the Spleen as concurring with the
glands of the absorbent system, in the assimilating process, by which
the crude nutritive materials are rendered fit to circulate in the blood;
and as the latter operate upon those which are taken up by the lac-
teals, so may the former exert their influence upon those, which have
been received into the veins, — separating them from the mass of the
blood, and delivering them to the lymphatics to be further elabo-
rated.

509. It is worthy of remark, that a Spleen is found in all Verte-
brated animals, which have a distinct Absorbent system ; but that no
organ exactly corresponding with it exists in the Invertebrata, which
are destitute of that system, — although the distensible cellated cavi-
ties, apparently destined to perform its safety-valve function, exist in
some of the higher among them. This is an additional reason for
regarding its parenchymatous portion as essentially a part of the assi-
milating apparatus of the Absorbent system.

510. The Supra-Re7ial Capsules seem to correspond with the Spleen
in their general structure, and in their connection with the Lymphatic
system ; whilst in the arrangement of their component parts, they bear
more resemblance to the Kidney. Their exterior or cortical portion is
formed of straight arteries, which divide into a minute capillary net-
work ; and from this arise venous branches, which form a minute
plexus, pouring its contents into a large central cavity, which is the
dilafed commencement of the supra-renal vein. No apparatus of
secreting tubes or vesicles can be detected in it ; but the interspaces
of the venous plexus are filled up with a sort of pulp consisting of
minute spherules, averaging about l-10,000th of an inch in diameter,
but varying from nearly twice that size to less than half. These
bodies appear to be the nuclei of cells, the full development of which
is checked ; but in the Ruminant animals, and occasionally in the
Human subject, the cells are more or less developed, and then re-
semble the ordinary lymph-corpuscles in size and appearance. The
Lymphatics are of large size, like those of the Spleen ; and probably
convey away the matter which has been elaborated by these organs,
that it may be mingled with that which is being taken up and pre-
pared by other parts of the Absorbent system. The Supra-Renal
capsules attain a very large size early in foetal life, surpassing the true
Kidneys in dimension, up to the tenth or twelfth week; but they
afterwards diminish relatively to the latter, and are evidently subor-

THYMUS GLAND. 297

dinate organs, during the whole remainder of life. It does not seem
unlikely that these bodies, like the Spleen, have a double function ;
and that, besides participating in the general actions of the Absorb-
ent glandulse, they may serve as a diverticulum for the Renal circu-
lation, when from any cause the secreting function of the Kidneys is
retarded or checked, and the movement of blood through them is
stagnated.

511. The Thymus Gland is another body, which seems referable
to the same group ; having all the essential characters of a true gland
(§ 714), save an excretory duct ; and its function being evidently
connected, during the early period of life at least, with the elaboration
of nutritive matter, which is to be re-introduced into the circulating
current. Its elementary structure may be best understood from the"
simple form it presents, when it is first capable of being distinguished
in the embryo. It then consists of a single tube, closed at both ends,
and filled with granular matter; and its subsequent development con-
sists in the lateral growth of branching off-shoots from this central
tubular axis. In its mature state, therefore, it consists of an assem-
blage of glandular follicles, which are surrounded by a plexus of
blood-vessels ; and these follicles all communicate with the central
reservoir, from which, however, there is no outlet. The cavities of
the follicles contain a fluid, in which a number of corpuscles are
found, giving it a granular appearance. These corpuscles are for the
most part in the condition of nuclei; but fully developed cells are
found among them, at the period when the function of this body
seems most active. " The chemical nature of the contents at this
period, closely resembles that of the ordinary proteine-compounds. —
It has been commonly stated, that the Thymus attains its greatest
development, in relation to the rest of the body, during the latter
part of fcetal life ; and it has been considered as an organ peculiarly
connected with the embryonic condition. But this is a mistake ; for
the greatest activity in the growth of this organ manifests itself, in the
Human infant, soon after birth ; and it is then, too, that its functional
energy seems the greatest. This rapid state of growth, however, soon
subsides into one of less activity, which merely serves to keep up its
proportion to the rest of the body ; and its increase usually ceases
altogether at the age of about two years. From that time, during a
variable number of years, it remains stationary in point of size ; but,
if the individual be adequately nourished, it gradually assumes the
character of a mass of fat, by the development of the corpuscles of its
interior into fat-cells, which secrete adipose matter from the blood.
This change in its function is most remarkable in hybernating Mam-
mals; in which the development of the organ continues, even in an
increasing ratio, until the animal reaches adult age, when it includes
a large quantity of fatty matter. The same is the case, generally
speaking, among Reptiles. It is an important fact in the history of
this organ, that it is not to be detected in Fishes ; and does not appear
to exist, either in the tadpole state of the Batrachian reptiles, or in the

298 THYMUS GLAND.— THYROID GLAND.

Perennibranchiate group ; so that we may regard it as essentially con-
nected with pulmonic respiration.*

512. Various facts lead to the conclusion, that the function of the
Thymus, at the period of its highest development, is that of elabo-
rating and storing up nutritive materials, to supply the demand which
is peculiarly active during the early period of extra-uterine life. The
elaborating action probably corresponds with that, which is exerted
by the glands of the Absorbent system ; and the product, as in the
preceding cases, seems to be conveyed away by the lymphatics. The
provision of a store of nutritive matter seems a most valuable one,
under the circumstances in which it is met with ; the waste being
more rapid and variable than in adults, and the supply not constant.
Thus it has been noticed that, in over-driven lambs, the thymus soon
shrinks remarkably; but that it becomes as quickly distended again
during rest and plentiful nourishment. As the demand becomes less
energetic, and as the supplies furnished by other organs become more
adequate to meet it, the Thymus diminishes in size, and no longer
performs the same function. It then obviously serves to provide a
store of material, not for the nutrition of the body, but for the respi-
ratory process, when this has to be carried on for long periods — as in
hybernating Mammals and in Reptiles — without a fresh supply of
food. — It is possible that the Thymus gland may further stand in the
same relation to the Lungs, as the Spleen to the Liver, and the Supra-
Renal capsules to the Kidneys ; that is, as a diverticulum for the
blood transmitted through the bronchial arteries (which are the
nutritive vessels of the Lungs), before the Lungs acquire their full
development in comparison with other organs, or when any cause
subsequently obstructs the circulation through their capillaries.

513. The Thyroid Gland bears a general analogy to the Thymus;
but its vesicles are distinct from each other, and do not communicate
with any common reservoir. They are surrounded, like the vesicles
of the true glands, with a minute capillary plexus ; and in the fluid
they contain, numerous corpuscles are found suspended, which appear
to be cell-nuclei, in a state of more or less advanced development.
This body is supplied with arteries of considerable size ; and with
peculiarly large lymphatics. Though proportionably larger in the
foetus than in the adult, it remains of considerable size during the
whole of life. It appears, from the recent inquiries of Mr. Simon, f
that a Thyroid gland, or some organ representing it in place and
office, exists in all Vertebrated animals. It presents its simplest form
in the class of Fishes; in some of which it appears to consist merely
of a plexus of capillary vessels, connected with the origin of the
cerebral vessels, and capable, by its distensibility, of relieving the
latter, in case of any obstruction to the proper movement of blood
through them. In the higher forms of this organ, the glandular
structure, — consisting of the closed vesicles over which the capillary

* See Mr. Simon's admirable Prize Essay on the Thymus Gland.
I Philosophical Transactions, 1844.

CHARACTERS OF CHYLE AND LYMPH. 299

plexus is distributed, and of their cellular contents, — is superadded :
and the organ then appears, like the Spleen, to be destined for two
different uses ; namely, to serve as a diverticulum to the Cerebral
circulation; and to aid in the elaboration of nutritive matter, which is
taken up by the Absorbent system, and which is again poured by it
into the general current of the circulation.

514. Thus the Spleen, the Supra-Renal Capsules, the Thymus
Gland, and the Thyroid Gland, all seem to share in the preparation
of the nutritive materials of the blood, along with the ordinary glan-
dulee of the Absorbent system. In fact, we may regard them all as
together constituting an apparatus, which is precisely analogous to
that of the ordinary glands, but of which the elementary parts are
scattered through the body, instead of being collected into one com-
pact structure. Thus if we could imagine any tubular gland, such
as the Kidney or the Testis, to be unraveled, and its convoluted
tubuli to be spread through the system, yet all discharging their con-
tents by a common outlet, we should have no unapt representation of
the Lymphatic portion of the Absorbent system. Its function appears
to be, to separate the crude Albuminous matter from the blood, to
subject it to an elaborating action performed by the epithelium-cells
lining the tubes, and then to pour forth this elaborated product, — not
as an excretion to be carried out of the body, — but (in conjunction
with that, w^hich has been newly taken in by the Lacteal portion of the
system, and which has undergone elaboration by its glandulse), into
the blood-vessels, which are to convey it to the different parts of the
body where it is to be appropriated. The four bodies we have been
just considering, appear to be, so far as their glandular function is
concerned, appendages to this system. Their uses as diverticula to
the circulation through other organs, render them liable to occasional
distension with blood ; and it seems determined that this blood shall
not lie useless, but shall be subservient to the action in question ; the
gland-cells that line the cavities of the organ withdrawing certain
constituents of the blood, to restore them, through the Lymphatic
system, in a state of more complete preparation for the operations of
Nutrition. Their function is very probably vicarious ; that is, the
determination of blood is greatest (through the state of the other
organs) at one time to one of these bodies, and at another time to
another. Hence the effects of the loss of any one of them are not
serious ; as the others are enabled in great degree to discharge its
duty.

4. Composition and properties of the Chyle and Lymph.

515. The chief chemical difference between the Chyle and the
Lymph, consists in the much smaller proportion of solid matter in the
latter, and in the almost entire absence of fat, which is an important
constituentof the former. This is well shown in the following com-
parative analyses, performed by Dr. G. 0. Rees, of the fluids obtained

30Q

CHARACTERS OF CHYLE AND LYMPH.

from the lacteal and lymphatic vessels of a donkey, previously to their
entrance into the thoracic duct ; the animal having had a full meal
seven hours before its death.

Water - - - .

Albuminous matter (coagulable by heat)
Fibrinous matter (spontaneously coagulable)
Animal extractive matter, soluble in water

and alcohol
Animal extractive matter, soluble in water

only ... -

Fatty matter - - -

Salts ; — Alkaline chloride, sulphate and car-
bonate, with traces of alkaline phosphate,
oxide of iron - - _

Chyle. Lymph.

90-237 95-536

3-516 1-200

0-370 0-120

0-332 0-240

1'233 1-319

3-601 a trace.

0-711 0-585

100-000 100-000

The Lymph obtained from the neck of a horse has been recently
analyzed by Nasse, with nearly the same result. He found it to con-
tain 95 per cent, of water ; and the 5 per cent, of solid matter was
chiefly composed of albumen and fibrin, with watery extractive, —
scarcely a trace of fat being to be found. The proportions of saline
matter were found to be remarkably coincident with those, which exist
in the serum of the blood ; as might be expected from the fact, that
the fluid portion of the lymph must have its origin in that which has
transuded through the blood-vessels: the absolute quantity, however,
is rather less. — A similar analysis of the Chyle of a cat by Nasse, has
given results very closely correspondent with that of Dr. Rees ; for
the proportion of water was 90-5 per cent. ; and of the 9-5 parts of
solid matter, the albumen, fibrin, and extractive amounted to more
than 5, and the fat to more than 3 parts. — Dr. Rees has also analyzed
the fluid of the Thoracic duct of Man ; which consists of chyle with
an admixture of lymph ; and he found this to contain about 90-5 per
cent, of water, 7 parts of albumen and fibrin, 1 part of aqueous
alcoholic extractive, and not quite 1 part of fatty matter with about J
per cent, of salines. The composition of this fluid more resembles
that of the lymph than that of the chyle ; the proportion of the fatty
to the albuminous matter being small. This was probably due to the
circumstance, that the subject from which it was obtained (an executed
criminal) had eaten but little for some hours before his death.

516. The characters of the Chyle are not the same in every part of
the Lacteal system; for the fluid undergoes a very important series of
changes in its characters, in its transit from the walls of the intestines
to the receptaculum chyli. The fluid drawn from the lacteals that
traverse the intestinal walls, has no power of spontaneous coagula-
tion ; whence we may infer that it contains little or no Fibrin. It
contains Albumen in a state of complete solution, as we may ascer-

PROGRESSIVE ALTERATIONS IN THE CHYLE. 301

tain by the influence of heat or acids in producing coagulation. And
it includes a quantity of fatty matter, which is not dissolved, but
suspended in the form of globules of variable size. The quantity of
this evidently varies with the character of the food ; it is more abund-
ant, for instance, in the chyle of Man and the Carnivora, than in
that of the Herbivora. It is generally supposed that the milky colour
of the chyle is owing to the oil-globules ; but Mr. Gulliver has pointed
out that it is really due to an immense multitude of far more minute
particles, w^hich he has described under the name of the molecular
base of the chyle. These molecules are most abundant in rich, milky,
opaque chyle ; whilst in poorer chyle, which is semi-transparent, the
particles float separately, and often exhibit the vivid motions common
to the most minute molecules of various substances. Such is their
minuteness, that, even wdth the best instruments, it is impossible to
determine either their form or their dimensions with exactness; they
seem, however, to be generally spherical ; and their diameter may
be estimated at between l-36,000th and l-24,000th of an inch.
Their chemical nature is as yet uncertain ; they are remarkable for
their unchangeableness, when submitted to the action of numerous
re-agents, which quickly affect the proper Chyle-corpuscles ; whilst
their ready solubility in Ether would seem to indicate that they are of
an oily or fatty nature.

517. The milky aspect which the serum of blood sometimes ex-
hibits, is due to an admixture of this molecular base. It may be par-
ticularly noticed, when blood is drawn a few hours after a full meal,
that has been preceded by a long fast. By recent experiments it has
been found, that the serum begins to show this turbidity, about half
an hour after the meal has been taken ; and that the turbidity increases
for some hours subsequently, after which it disappears. The period
at which the discoloration is greatest, and the length of time during
which it continues, vary according to the digestibility of the food.
When the serum is allowed to remain at rest, the opaque matter rises
to the surface, presenting very much the appearance of cream; and
when separately examined, it has been found to contain a proteine-
compound, mingled with oily matter, — the relative amount of the
two appearing to depend in part upon the characters of the food in-
gested. Hence it would not seem improbable, that the molecular
base of the chyle is partly derived from albuminous matter of the
food, which has not been completely dissolved in the digestive pro-
cess, but which has been reduced to a state of exceedingly minute
division (§ 473). The gradual disappearance of the turbidity of the
serum indicates that the substance which occasioned it no longer
exists as such in the circulating current ; being either drawn off* by
the nutritive or secretory operations, or being converted by the as-
similating process into the ordinary constituents of the blood.

518. During the passage of the Chyle along the lacteals, towards
the Mesenteric glands, it undergoes two important changes ; the pre-
sence of Fibrin begins to manifest itself by the spontaneous coagula-

302 PROGRESSIVE ALTERATIONS IN THE CHYLE.

bility of the fluid ; and the oil-globules diminish in proportional
amount. The fibrin appears to be formed at the expense of the albu-
men; as this latter ingredient undergoes a slight diminution. It is
in the chyle drawn from the neighbourhood of the mesenteric glands,
that we first meet with the peculiar floating cells or chyle-corpuscles,
formerly adverted to (§ 212), in any number. The average diameter
of these is about l-4600th of an inch ; but they vary from about
l-700th to l-2600th,— that is, from a diameter about half that of the
human blood-corpuscles, to a size about a third larger. This varia-
tion probably depends in great part upon the period of their growth.
They are usually minutely granulated on the surface, seldom exhibit-
ing any regular nuclei, even when treated with acetic acid ; but three or
four central particles may sometimes be distinguished in the larger ones.
These corpuscles are particularly abundant in the chyle obtained by
puncturing the mesenteric glands themselves ; and there can be little
doubt, that they are identical with the altered epithelium-cells, which
line the lacteal tubes in their course through those bodies (§ 496).

519. The glandular character of these cells, and their continued
presence in the circulating fluid, seem to indicate that they have an
important concern in the process of Assimilation, — that is, in the
conversion of the crude elements derived from the food, into the
organizable matter adapted to the nutrition of the body; in other
words, in the conversion of Albumen into Fibrin ; which change
would seem to take place to a considerable extent in the Mesenteric
glands. For it is only in the Chyle which is drawn from the lacteals
intervening between the mesenteric glands and the receptaculum
chyli, that the spontaneous coagulability of the fluid is so complete as
to produce a perfect separation into clot and serum. The former is a
consistent mass, which, when examined with the microscope, is found
to include many of the chyle-corpuscles, each of them being sur-
rounded with a delicate film of oil ; the latter bears a close resemblance
to the serum of the blood, but has some of the chyle-corpuscles sus-
pended in it. Considerable differences present themselves, however,
both in the perfection of the coagulation, and in its duration. Some-
times the chyle sets into a jelly-like mass ; which, without any sepa-
ration into coagulum and serum, liquefies again at the end of half an
hour, and remains in this state. The coagulation is usually most
complete in the fluid drawn from the receptaculum chyli and thoracic
duct; and here the resemblance between the floating cells, and the
white or colourless corpuscles of the blood, becomes very striking.

520. The Lymph, or fluid of the Lymphatics, differs from the
Chyle, as already remarked, in its comparative transparency : its
want of the opacity or opalescence, which is characteristic of the
latter, being due to the absence, not merely of oil-globules, but also
of the "molecular base." It contains floating cells, which bear a
close resemblance to those of the Chyle on the one hand, and to the
colourless corpuscles of the Blood on the other; and these, as in the
preceding case, are most numerous in the fluid, which is drawn from

ABSORPTION FROM EXTERNAL AND PULMONARY SURFACE. 303

the lymphatics that have passed through the glands, and in that ob-
tained from the glands themselves. Lymph coagulates like chyle ;
a colourless clot being formed, which encloses the greater part of
the corpuscles. The Lacteals may be regarded as the Lymphatics of
the intestinal walls and mesentery ; performing the function of inter-
stitial absorption, as well as effecting the introduction of alimentary
substances from without. During the intervals of digestion, they
contain a fluid, which is in all respects conformable to the lymph of
the lymphatic trunks.

521. Thus by the admixture of the aliment newly introduced from
without, with the matter which has been taken up in the various
parts of the system, and by the preparation which these undergo in
their course towards the thoracic duct, a fluid is prepared, which
bears a strong resemblance to blood in every particular, save the
presence of red corpuscles. Even these may sometimes be found in
the contents of the thoracic duct, in sufficient amount to communi-
cate to them a perceptible red tinge ; but there can be little doubt
that they have found their way thither accidentally, — some of the
lymphatic or lacteal trunks, which have been divided in the dissec-
tion necessary to expose the duct, having taken up blood by their
open mouths, and rapidly transmitted it into the general receptacle.
The fluid of the thoracic duct may be compared to the blood of
Invertebrated animals ; from which the red corpuscles are almost or
altogether absent ; but which contains white or colourless corpuscles,
and which possesses but a slight coagulating power, in consequence
of its small proportion of fibrin. And we hence see, why these
animals should require no special absorbent system ; since the blood-
vessels convey a fluid, which is itself so analogous to the chyle and
lymph to be absorbed, that the latter may be at once introduced into
it, without injuring its qualities.

5. Absorption from the External and Pulmonary Surface.

522. Although the Mucous Membrane of the Alimentary Canal is
the special channel for the introduction of nutritive or other sub-
stances into the system, it is by no means the only one. The Skin
covering the body, and the Mucous Membrane prolonged into the
Lungs, are also capable of absorbing liquids and vapours, and of
introducing them into the Circulation; although they serve this pur-
pose less in Man and the higher animals, than in some of the lower.
Their utility in this respect is best shown, when, from peculiar cir-
cumstances, the function of the digestive cavity cannot be properly
performed; and when, therefore, the system has been more than
usually drained of its fluids, and stands in need of a fresh supply. —
Thus shipwrecked sailors, and others, who are suffering from thirst,
owing to the want of fresh water, find it greatly alleviated, or alto-
gether relieved, by dipping their clothes into the sea, and putting
them on whilst still wet, or by frequently immersing their own

304 COMPOSITION OF THE BLOOD.

bodies. In a case of dysphagia, in which neither solid nor fluid
nutriment could be introduced into the stomach, the patient was kept
alive for a considerable time, and his sufferings greatly alleviated, by
the administration of nutritive clysters, and by the immersion of his
body in a bath of tepid milk and water, night and morning. Under
this system, the weight of the body, which had previously been
rapidly diminishing, remained stationary, although the amount of
the excretions was increased ; and the use of the bath had a special
influence in assuaging the thirst, which was previously distressing.
It appeared that the w^ater of the urinary excretion, amounting to
from 24 oz. to 36 oz. per day, must have been entirely supplied from
this latter source. Again, a man who had lost nearly 3 lbs. by per-
spiration, during an hour and a quarter's labour in a very hot atmo-
sphere, regained 8 oz. by immersion in a warm bath at 95° for half
an hour. — In these cases it appears probable, from the experiments
already noticed (§ 502), that the Lymphatics, rather than the blood-
vessels, are the chief agents in the absorbing process ; not, however,
from any powers peculiar to them, but merely on account of the
thinness of their walls, and their very copious distribution in the
skin.

523. Absorption may also take place from an atmosphere saturated
with watery vapour. Of this we have a very curious proof in the
Frog; whose urinary bladder (which serves as a sort of reservoir of
water) has been observed to be refilled, after having been emptied,
by placing the animal in an atmosphere loaded with watery vapour.
Numerous instances are on record, which prove that such absorption
may take place in Man, to a very considerable extent; though the
proportion introduced through the Skin, and through the Lungs,
cannot be exactly ascertained. The ready introduction of volatile
matter into the system, through the latter channel, is a matter of
familiar experience ; thus if w^e breathe an atmosphere through which
the vapour of turpentine is diffused, it soon produces the character-
istic odour of violets in the urinary secretion. And it is probably in
this manner, that a large number of those poisonous miasmata are
introduced, which are such fertile causes of disease.

6. Of the Composition and Properties of the Blood.

524. Having traced the steps by which the blood is elaborated, and
prepared for circulation through the body, and having (in the former
part of the volume) inquired into the characters of its chief constitu-
ents, w-e have now^ to consider the fluid as a w^hole, to study the usual
proportions of these constituents, and the properties which they im-
part to it.

525. The Blood, whilst circulating in the living vessels, may be
seen to consist of a transparent, nearly colourless fluid, termed liquor
sanguinis; in which the corpuscles^ to which the blood owes its red
hue, as well as the white or colourless corpuscles, are freely suspended

COMPOSITION OF THE BLOOD. 305

and carried along by the current. — On the other hand, when the blood
has been drawn from the body, and is allowed to remain at rest, a
spontaneous coagulation takes place, separating it into clot and serum.
The clot is composed of a network of Fibrin, in the meshes of w^hich
the Corpuscles, both red and colourless, are involved ; and the serum
is the same w^ith the liquor sanguinis deprived of its Fibrin. When
the Serum is heated, it coagulates, showing the presence oi Albumen,
And if it be exposed to a high temperature, sufficient to decompose
the animal matter, a considerable amount of earthy and alkaline salts
remains. — Thus we have four principal components in the Blood ; —
namely, Fibrin, Albumen, Corpuscles, and Saline matter. In the
circulating Blood they are thus combined : —

Fibrin ^

Albumen > In solution, forming Liquor Sanguinis.

Salts )

Red Corpuscles, — Suspended in Liquor Sanguinis.

But in coagulated blood they are thus combined : —

Fibrin

-r, , >^ ■, i Crassamentum or Clot.

Ked Corpuscles J

Albumen ? d ... i ,. r • o

<^ , > Remaming in solution, lorming Serum.

A certain amount of Serum, however, is involved in the Crassa-
mentum ; and can only be separated by cutting the clot into thin
slices, and carefully washing it.

526. The components of the Blood may be separated, and their
amount estimated, in various w^ays. Thus, if fresh-drawn blood be
continually stirred with a stick, or be *' whipped," with a bunch of
twigs, the Fibrin coagulates in the form of strings, which adhere to
the wood, and may thus be withdrawn ; whilst the red corpuscles then
remain suspended in the serum, gradually sinking to the bottom in
virtue of their greater specific gravity. — On the other hand, the Red
Corpuscles may be separated, in those animals in which they are large
enough, by passing the blood through a filter ; having previously min-
gled with it some substance, w^hich retards, but does not prevent its
coagulation* (§ 185). The liquor sanguinis is thus separated from the
blood-discs ; and the former coagulates, whilst the blood-discs are
retained upon the filter. This experiment convincingly proves, that
the act of coagulation is not due to the red corpuscles, as was at
one time imagined. The ordinary act of coagulation, by w^ithdraw-
ing the Fibrin and Corpuscles, makes it easy to estimate the propor-
tion of Albumen and of Saline matter in the Blood, when due allow-
ance is made for the quantity of Serum retained in the Clot; and the
relative proportions of these may be determined, by evaporating the

* This experiment cannot be performed with Human blood, because the corpuscles
are small enough to pass through the pores of any filter that allows the liquor san-
guinis to permeate it ; but it answers very well with Frog's blood.

20

306 COMPOSITION OF THE BLOOD.

fluid, SO as to obtain the whole amount of solid matter it contains, and
by then calcining the residuum, so as to ascertain how much of this is
a mineral ash, — the remainder being chiefly Albumen. — The solid
matter of the blood also contains various Fatty substances, which
may be removed from it by ether. Some of these appear to corre-
spond with the constituents of ordinary Fat (§ 261); whilst another
contains phosphorus, and seems allied to the peculiar fatty acids of
Neurine (§ 383); and another has some of the properties of Choles-
terine, the fatty matter of the Bile (§ 724). — Besides these, there are
certain substances known under the name of Extractive; one group
of which is soluble in water and another in Alcohol. Of the precise
nature of these, little is known. They have been aptly termed '' ill-
defined" animal principles ; and it is probable that they may include
various substances in a state of change or disintegration, which are
being eliminated from the Blood by the processes of Excretion.

527. The general result of numerous recent analyses of the Blood
may be thus stated : — The whole amount of solid matter is greater in
the Male than in the Female. The higher proportion extends to all
its components except the Albumen ; and this is almost invariably
present in an amount, which is absolutely greater in 1000 parts of
female blood, than in 1000 parts of that of the male, and which is
considerably greater in proportion to the other solid matters. The
proportion of Albumen seems more constant than that of the other
constituents of Blood; seldom varying beyond 5 or 6 parts either
more or less than 70 in 1000. — The quantity of Corpuscles appears
liable to considerably greater variation ; the superiority on the side of
the Male, however, being very strongly marked in the maximum and
minimum, as well as in the average. We may regard its average
in the Male at about 140 in 1000 parts of blood ; but it may fall to
110-5 parts, without the health being seriously aflected ; whilst, on
the other hand, it may arise to 186 without any manifestation of dis-
ease. In the Female, its average may be about 112 parts in 1000;
but it may fall to as little as 71-4, and may rise to 167, consistently
with ordinary health. The range of variation is thus much greater in
the Female than in the Male; the minimum being considerably less
in the former, than half the maximum ; whilst in the latter, it is much
more. This is probably due in part to the fact, that the loss by the
Catamenial discharge may produce a great temporary depression in the
proportion of the corpuscles. — The average proportion of Fibrin seems
to be no more than 2*2 in the Male; and though it may rise to as
much as 3*5 or even 4, without disordering the system, it does not
seem to fall below 2, in the state of ordinary health. The average in
the Female is probably about 2; the proportion may rise to 3, or fall
to 1*8; but the variation seems less considerable in the Female than
in the Male. — Much is probably yet to be learned, regarding the influ-
ence of different kinds of food recently taken, on the proportion of
these constituents of the blood ; and it does not seem unlikely, from
what has been already stated (§ 517), that the quantity of fatty matter

COMPOSITION OF THE BLOOD. 307

is especially liable to variation, in accordance with the amount con-
tained in the food, and the time which has elapsed since the last meal.

528. The Saline constituents of the blood, obtained by drying and
incinerating the whole mass, usually amount to between 6 and 7 parts
in 1000. More than half of their total quantity is composed of the
Chlorides of Sodium and Potassium ; and the remainder is made up
of the tribasic Phosphate of Soda, the Phosphates of Lime and Mag-
nesia, Sulphate of Soda, and a little Phosphate and Oxide of Iron.
Of these the chief part are dissolved in the Serum ; but the Earthy
Phosphates, which are insoluble by themselves, are probably com-
bined with the proteine-compounds (§ 175); and the iron is contained,
chiefly or entirely, in the red corpuscles. It is difficult to speak with
certainty, from the examination of the ashes of the blood, as to the
state of the saline constituents of the circulating fluid. Thus, the
Serum has an alkaline reaction ; and this has been supposed to be due
to the presence of alkaline Carbonates. Moreover, the presence of
the Lactates of potash and soda has been usually asserted. On the
other hand, some recent analyses would indicate, that the alkaline
reaction is entirely due to the presence of the tribasic Phosphate of
soda ; and that no alkaline carbonates or lactates exist in the blood.
This discrepancy seems partly due to the mode of analysis employed ;
for it has been lately pointed out by Dr. G. O. Rees, that although
the ashes of the entire mass of blood do not efl^ervesce on the addition
of an acid, effervescence takes place, when acid is added to the ashes
of the Serum ; showing the existence in it, either of alkaline Carbon-
ates, or of Lactates which have been reduced to the state of Carbon-
ates by incineration. It appears that when the entire mass of blood
is incinerated, enough phosphoric acid is produced from the phos-
phorized fats, to neutralize the alkaline carbonates, and thus to pre-
vent their presence from being recognized. There can be no doubt,
however, that the tribasic phosphate of soda exists as such in the
blood, and contributes to its alkaline reaction ; and it appears to con-
fer upon the serum a special power of absorbing carbonic acid.

529. The following appear, from the considerations stated in the
preceding part of the Volume, to be the chief uses of the principal
constituents of the Blood, in the general economy. The Fibrin is
the material, which is most completely prepared for organization, and
which supplies what is requisite for the nutrition of the larger pro-
portion of the solid tissues of the body. It is, therefore, being con-
tinually withdrawn from the blood by the nutritive operations ; and
the demand appears to be supplied, in part by the influx of Fibrin
that has been prepared in the Absorbent system, and in part by the
continued transformation of Albumen, which takes place during the
Circulation of the Blood. If a proper amount of Fibrin be not pre-
sent in the Blood, its physical properties are so far altered, by the
diminution of its viscidity, that it will not circulate through the capil-
laries as readily as before, — a certain degree of viscidity having been
experimentally found to be favourable to the movement of fluid

308 COMPOSITION OF THE BLOOD.

through glass or metallic tubes of small bore. — The Albumen of the
blood is the raw material, at the expense of which not only the Fi-
brin, but many other substances are generated during the nutritive
process. All the Albuminous compounds of the Secretions, the
Horny matter of the Epidermic tissues, the Gelatin of the simple
fibrous tissues, the solid materials of the Red Corpuscles, and other
substances, may be regarded as almost certainly produced by the
transformation of the Albumen of the Blood ; and a continual supply
of this from the food is therefore requisite, to preserve the due pro-
portion in the circulating fluid. — The Red Corpuscles, which (it will
be remembered) are almost exclusively confined to Vertebrated ani-
mals, appear to be more connected with the function of Respiration,
than with that of Nutrition ; and the stimulating action of Arterial
blood, especially upon the Muscular and Nervous tissues, appears
chiefly to depend upon their presence. It has been observed in
particular, that their presence is more effectual in stimulating the
heart's action, than is that of either of the other constituents of the
blood. In addition to what has been already stated (§ 219), in re-
ference to their continual disintegration and renewal, it may be men-
tioned, that when the blood of one animal was injected by Majendie
into the veins of another having discs of very different size and form,
the original Red corpuscles soon disappeared, and were replaced by
those characteristic of the species, in whose veins the fluid was cir-
culating.

530. The use of the Saline matter is evidently in part to prevent
decomposition in the circulating Blood ; but also to supply the mineral
materials, requisite for the generation of the tissues, and entering into
the composition of the secretions. It is by the saline and albuminous
matters in conjunction, that the specific gravity of the Liquor Sangui-
nis is kept up to the point, at which it is equivalent to that of the
contents of the Red Corpuscles ; and it is only in this condition, that
the formation of the latter can duly take place. — The Fatty matters
of the Blood are evidently derived from the food, either directly, or
by a transformation of its farinaceous ingredients (§ 430) ; and they
are chiefly appropriated to the maintenance of the combustive process.
That which may be superfluous is either deposited in the cells of Adi-
pose Tissue, or it is eliminated by the Liver, the Sebaceous follicles
of the Skin, and, in the female when nursing, by the Mammary glands.
The blood appears to contain, ready formed, the peculiar azotized and
phosphorized fat of Nervous matter; but how this is generated, —
whether by the combination of azotized and phosphorized ingredients
with ordinary fat, or by the metamorphosis of albuminous matter, —
cannot be said to be yet determined.

531. The proportion of these components of the Blood is liable to
undergo changes in disease, which extend far beyond the widest limits
which have been mentioned as consistent with health. Thus, the
quantity of Fibrin exhibits a remarkable increase in Inflammation ;
the amount then found in the blood being from 5 or 6 parts in 1000

COMPOSITION OF BLOOD IN DISEASE. 309

to 9, 10, or even lOJ, according to the extent and intensity of the
disease. On the other hand, it presents a remarkable diminution in
Typhoid fevers ; the quantity being sometimes as little as 0-9. If
any decided Inflammation should develop itself, however, in the
course of the Fever, the proportion of Fibrin rises accordingly. A
deficiency of Fibrin in the blood predisposes to Hemorrhages, Con-
gestions, &c., either into the substance of the tissues, or on the surface
of membranes ; and these conditions are well known to be of frequent
occurrence as complications of febrile disorders. An excess of Fibrin
is not much affected by copious bleeding, even if this be frequently
repeated ; but there is reason to think, that the administration of
Mercury has a tendency to restrain its production.

532. It is difficult to say what amount of Red Corpuscles should be
regarded as excessive ; since, as we have seen, they may augment to
a great degree, without disturbing the health. When they are present
in an amount much above the average, they seem concerned in pro-
ducing the condition termed Plethora ; which marks a '' high condi-
tion" of the system, and which borders upon various diseases, espe-
cially those of Congestion, and Hemorrhages. To these a peculiar
liability then exists ; because, although the proportion of Fibrin in
the blood is not absolutely low, it is low in reference to that of the
Red Corpuscles. Plethoric persons do not seem more liable to In-
flammation, than are those of weakly constitution. The quantity of the
Red Corpuscles is rapidly diminished by frequent bleeding ; and hence
it is lowered by repeated Hemorrhages. On the other hand, it is
speedily restored to its usual standard under the influence of nutritious
diet, if the digestive powers have not been too much weakened to
make use of this. — The proportion of Red Corpuscles undergoes a
marked diminution in various forms of Ansemia ; and particularly in
Chlorosis. In severe cases of this latter disease, it has been found as
low as 27 in 1000 ; and it not unfrequently sinks to 40 or 50. The
marked influence of the administration of Iron, in favouring the repro-
duction of Red Corpuscles, has been already noticed (§ 219).

533. The proportion of Albumen in the Blood seems less liable to
change, except in the condition termed Albuminuria, in which a large
quantity of Albumen appears in the Urine. When this condition is
permanently established, it is indicative of the existence of serious
organic disease of the kidney ; but it may occur for a short time under
the influence of simple congestion of that organ, w^hich causes an
escape of the albuminous part of the blood, together with the water
which is filtered-off (as it were) in this gland (§ 728). Now when
Albuminuria is fully established, there is a marked diminution in the
quantity of Albumen in the serum of the blood ; and this diminution
is constantly proportional to the amount of Albumen present in the
Urine. The proportion of Saline matter appears to undergo less altera-
tion in disease than that of the other constituents of the Blood ; and
has not been found to have a regular correspondence, either in the
way of excess or diminution, with any particular morbid state.

310 COAGULATION OF BLOOD.

534. The condition of the Blood may be affected, not merely by
alteration in the proportions of its normal ingredients, but by the pre-
sence of other substances ; — either such as are generated in it, and
are constantly being eliminated from it in health, but have accumu-
lated to an abnormal degree ; — or such as have found their way into
it from without. Thus, Carbonic Acid, Urea and Lithic Acid, Cho-
lesterine and other elements of Bile, and other matters which it is the
office of the Excreting organs to remove, may accumulate in the blood,
and may become fertile sources of disease, by their injurious influence.
The introduction of various Mineral substances, by absorption from
without, changes the composition of the normal elements of the Blood,
and thus affects their vital properties; thus strong saline solutions
diminish or destroy the coagulating power of the Fibrin. But the
most remarkable cases of depravation of the Blood, by the introduc-
tion of matters from without, are those which result from the action of

ferments^ — exciting such Chemical changes in the constitution of the
fluid, that its whole character is speedily changed, and its vital pro-
perties are altogether destroyed. Of such an occurrence we have a
marked example in the various forms of malignant fevers ; in which
the introduction of a very minute quantity of noxious matter into the
blood, either through the lungs or through the skin, produces a speedy
alteration in the characters of the whole mass of the blood, the func-
tion of every organ in the body is disordered, and decomposition of
the solids and fluids takes place to a considerable extent, even before
circulation ceases, and whilst consciousness yet remains. The train
of symptoms produced by the bite of venomous Serpents, and of rabid
animals, appears referable to the same cause, — the alteration in the
condition of the whole current of blood, by the introduction of a minute
quantity of a substance that acts as a ferment.

535. The Coagulation of the Blood, as already explained, depends
upon the passage of its Fibrin from the fluid state to the solid (§ 184} ;
consequently, if the fibrin be separated from the other elements, no
coagulation takes place. On the other hand, if the amount of Fibrin
be larger than ordinary, the coagulum possesses an unusual degree
of firmness. The length of time which elapses before coagulation,
and the degree in which the Clot solidifies, vary considerably; in
general they are in the inverse proportion to each other. Thus, if a
large quantity of blood be withdrawn from the vessels of an animal
at the same time, or within short intervals, the portions that last flow
coagulate much more rapidly, but much less firmly, than those first
obtained, in consequence of the diminished proportion of fibrin. On
the other hand, when the fibrin is in excess, its coagulation is un-
usually delayed. From this delay an important change results, in
the mode in which the coagulation takes place; for the red corpus-
cles, instead of being uniformly diffused through the coagulum, have
time to sink to the bottom, in virtue of their greater specific gravity;
and the upper part of the clot is consequently made up of Fibrin,
almost exclusively, whilst the lower is chiefly formed by the aggre-

BUFFY COAT.

311

gation of the red corpuscles. Hence the upper layer is almost desti-
tute of colour, (whence it has received the name of huffy coatj) and
is remarkably tenacious in its character; whilst the lower is very
deep in hue, and very friable in consistence. When the fibrillated
network forming the buffy coat undergoes the slow contraction, which
is characteristic of highly-elaborated fibrin subsequently to its coagu-
lation, it draws in the edges of the upper surface of the clot, giving
it a cupped appearance.

536. The BufTy Coat may present itself under a great variety of
conditions ; and it can no longer, therefore, be regarded as it formerly
was, a sign of the Inflammatory state. It is most fully developed
when acute Inflammation exists ; because in that condition all the cir-
cumstances which favour it are present. That it may be produced
by any cause, which occasions delay in the coagulation of the blood,
is evident from the fact, that healthy blood may be made to exhibit
it, by adding a solution of a neutral salt, which retards, but does not
prevent its coagulation. But the blood may coagulate with its ordi-
nary rapidity, or even more speedily than usual ; and may yet exhibit
the Bufiy Coat. And, moreover, the separation of the Fibrin and
the Red Corpuscles may take place in films of blood so thin, as not
to admit of a stratum of one being laid over the other; the two
elements separating from each other laterally, and the films acquiring
a speckled or mottled appearance, equally characteristic of the In-
flammatory condition with the BuflTy coat itself. Hence the separa-
tion must be due in such cases to other causes than gravity, and
recent observations have ac-
counted for it, by showing that
the Red Corpuscles have an un-
usual attraction for one another
in the Inflammatory state, causing
their coalescence in piles and
masses; whilst the particles of
Fibrin have also a peculiarly
strong attraction for each other.
Thus there is a powerful tend-
ency, that draws together the
components of each kind, and
consequently tends to separate
them from the others ; and when
this separation takes place, the
difference in the specific gravity
of the two elements decides
their respective situations. — The
peculiar tendency of the Red
corpuscles to unite, in the In-
flammatory state, serves to dis-
tinguish this condition, even in a single drop of blood ; and it is
then that the White corpuscles may be most easily distinguished, as

Fig. S2.

The microscopic appearance of a drop of blood
in the inflammatory condition. The red corpus-
cles lose their circular form, and adhere together;
the white corpuscles remain apart, and are more
abundant than usual.

312 CIRCULATION OP BLOOD.

they are seen apart from the rest of the mass, having no tendency to
unite with it. In fact, the white corpuscles are not found in com-
pany with the red, in the ordinary coagulum, but rather with the
fibrinous portion ; and when they are peculiarly abundant, as they
usually are in Inflammatory blood, they may form a considerable pro-
portion of the buflfy coat.

537. The BufTy Coat may present itself, without the least increase
in the normal quantity of Fibrin, and without any approach to the
Inflammatory state ; simply because the Fibrin is present in exces-
sive amount, in relation to the amount of Red corpuscles, the latter
being much below their usual proportion. Thus in severe Chlorosis,
the huffy coat is almost as strongly marked as in the severest Inflam-
mation ; but the two conditions are at once distinguished by the rela-
tive proportions of solid matter in the blood, as indicated by the size
of the Coagulum. For in Chlorosis the coagulum is very small, in
consequence of the reduced proportion of Corpuscles, and is almost
invariably found floating in the serum ; whilst in the ordinary Inflam-
matory condition, it is of full size, frequently adhering to the side of
the vessel.

CHAPTER VI.

OF THE CIRCULATION OF THE BLOOD.

1. JVature and Objects of the Circulation of JSTutrient Fluid.

538. The nutritive fluid, — the elements of which are thus chiefly
taken up by the Absorbent system, and are there prepared, as by
glandular apparatus diffused through the whole body, to be mingled
with the general mass of the previously-formed Blood, — is carried into
the various parts of the system, by the act of Circulation. This move-
ment answers various purposes. It furnishes all the tissues, which are
to derive nutriment from the Blood, with a constantly renewed supply
of the materials which they severally require ; and in this manner it
is subservient to the growth, not only of those tissues which form
part of the solid structure of the body, but also of those various cells,
covering its free surfaces, which are being continually cast off* and
renewed, and which, in the course of their development, separate from
the blood the products that are to perform ulterior purposes in the
economy, or are to be cast oflf as altogether effete. Thus the Circu-
lation is subservient to the functions of Nutrition and Secretion. In
the exercise of these functions, different materials are drawn from the
blood by the several tissues it supplies. Thus the nutrition of the
muscle requires fibrin ; that of the nerve requires fatty-matter; that of

CIRCULATION OF BLOOD. 313

the bone draws off gelatin and earthy salts ; that of the hepatic cells
removes the fatty matter and other elements of bile ; that of the milk-
cells (during lactation) separates albuminous, fatty, and saccharine
substances ; — and so on. Thus various portions of the blood, when
returning from the several organs through which they have been trans-
mitted, have undergone very different changes by the nutritive and
secreting processes, according to the function of the organs which they
have supplied ; and if the same portion of the circulating fluid were
constantly being transmitted to each organ, and returned from it, its
composition would speedily undergo a change that would render it no
longer fit for its purposes. By the union of the different local circu-
lations, however, into one general circulation, this change is pre-
vented, and the whole mass of the blood is maintained in its normal
or regular condition ; for as its composition is such, as to supply all
parts of the body, in a state of health, with the proportions of nutri-
tive material which they respectively need, and as the returning cur-
rents are all mingled together in the vessels, before being again dis-
tributed to the system, each part supplies what the other has been
deprived of, and thus the normal proportion of ingredients in the
whole mass of the blood is constantly kept up, whilst in each of its
separate streams it is undergoing an alteration of a different kind.

539. But these processes alone might be carried on by the aid of
a much less rapid Circulation, than that which exists in Man and the
higher animals. We do, in fact, occasionally meet with examples, in
which they continue for some time, under an almost total stagnation
of the current. There are others, however, which require a much
more rapid and uninterrupted movement of the circulating fluid. We
have already seen that, for the action of the Nervous and Muscular
tissues, oxygen is necessary ; and the amount of that gas contained in
the blood circulating through these tissues would be very speedily
exhausted, if it were not continually renewed ; whilst the carbonic
acid, which is formed at the expense of that oxygen, would speedily
accumulate to an injurious degree, if it were not carried off as fast as
it is produced. Hence we find that in all Animals, the maintenance
of the Respiration, by carrying Oxygen from the respiratory surface
into the different parts of the system, and by conveying back Carbonic
acid to be thrown ofl' at the Respiratory surface, is one of the great
purposes of the Circulation of the blood ; and its extreme importance
is shown by the very speedy check, which the interruption of this
function produces in the movement of the blood, in warm-blooded
animals. Thus in a Bird or Mammal, completely cut off from
Oxygen, the circulation in the lungs will come to a stop, which stop-
page will necessarily extend itself over the whole body, in little more
than three minutes.' We find, then, that the rate of the Circulation
in different animals, bears a relation to the energy of their Respiration ;
and this energy is closely connected with the general activity of their
functions, but particularly with that of the Nervous and Muscular
systems, which are most dependent for the exercise of their powers,

314 ASCENT OF SAP IN PLANTS.

upon a continually fresh supply of oxygen, and upon the unceasing
removal of the carbonic acid which is generated in their substance.

2. Different forms of the Circulating Apparatus.

540. It is desirable that the Circulating apparatus should be first
studied in its very simplest form, — that which it possesses in Plants
and in the lowest tribes of Animals ; as in this way alone can the
forces, which are concerned in the movement of the fluid, be rightly
appreciated. There are, in all the higher Plants, two distinct cur-
rents, that of the ascending^ and that of the descending sap. The
former of these fluids should be compared rather with the chyle than
with the blood of Animals ; for it is a crude fluid, not yet prepared to
take part in the nutrition and extension of the structure. But there
are some circumstances attending its movement, which throw light
upon other more complicated phenomena. The ascending sap con-
sists principally of water ; which is imbibed, together with various
substances which it holds in solution, by the delicate tissue at the soft
extremities of the root-fibres, or spongioles. The power of forcing
upwards a column of sap, which exists in these bodies, and which
seems due to Endosmose (§ 491), is shown by very simple experi-
ments. If the stem of a Vine, or of any tree in which the sap rises
rapidly, be cut across when in full leaf, the sap continues to flow from
the lower extremity ; and this with such force, as to distend with vio-
lence, or even to burst, a bladder tied firmly over the cut surface. If
instead of a bladder, a bent tube be attached to this, and mercury be
poured into it so as to indicate the pressure exerted, it is found that
the rise of the sap takes place with a force equal to the pressure of
from one to three atmospheres (from 15 to 45 lbs. upon the square
inch) — or even more. Thus the ascent of the sap is partly due to a
powerful vis a tergo, or impelling influence, derived from the point
where the absorption takes place.

541. But, on the other hand, if the upper extremity be placed with
the cut surface of the stem in water, a continued absorption of that
fluid will take place, as is evidenced by the withdrawal of the water
from the vessel ; the fluid which is thus taken up, however, is not
retained w^ithin the stem and branches, but is carried into the leaves,
and is thence dissipated by exhalation. It is obvious, then, that the
vis a tergo is not the sole cause of the ascent of the sap ; but that a
vis afronte also exists, by which the fluid is drawn towards the paVts
in which it is to be employed. This is further made apparent by a
few simple experiments. If a branch, when thus actively absorbing
fluid, be carried into a dark room, the absorption and ascent of fluid
immediately cease almost completely ; and are renewed again, so soon
as the leaves are again exposed to light. Now w^e know, from other
experiments, that light stimulates the exhaling process (§ 87), whilst
darkness checks it; and the cessation of the demand in the leaves
thus produces a cessation in the absorption at the lower extremity of

ASCENT AND DESCENT OF SAP IN PLANTS. 315

the stem. And this is the case also, in the natural condition of the
plant; as is easily shown by immersing the roots in water, and ob-
serving the respective quantities which are removed by absorption
during sunshine, shade, and darkness. On the other hand, the move-
ment of the sap may be excited, when it would not otherwise take
place, by the production of a demand at the extremities of the
branches; thus if a branch of a vine growing in the open air, be
introduced into a hot-house, and be subjected to artificial heat during
winter, its buds will be developed, its leaves will expand, and these
will draw fluid to themselves through the roots and stem, which are
still inactive as regards the remainder of the tree. And the natural
commencement of the movement of the ascending sap, which takes
place with the returning warmth of spring, has been experimentally
shown to occur, in the first instance, not in the neighbourhood of the
roots, but nearest the extremities of the branches ; the exhalation of
fluid from the expanding buds being the first process, and a demand
for fluid being thus created, which is supplied by the flow that is thus
excited in the lower part of the stem, — this, again, being supplied
from the roots, which are thus caused to recommence their absorbent
function.

542. Thus we see that, in the ascending sap, the movement is en-
tirely regulated by the demand for fluid, occasioned by the actions of
the leaves ; even though it is in great part dependent on the vis a tergo,
which has its seat in the spongioles. Not even this force, however,
— powerful as it has been shown to be, — can produce the continu-
ance of the upward flow, when the exhalation from the leaves is
checked by darkness, and when the demand occasioned by the action
of these organs is consequently suspended.

543. The movement of the descending sap offers numerous points,
which deserve to be carefully considered. This fluid is strictly com-
parable to the blood of animals; having undergone a preparation or
elaboration in the leaves, which adapts it to the nutrition and exten-
sion of the structure, and to the formation of the various secretions
of the plant. A great part of the fluid of the ascending sap has been
lost by exhalation ; and the remainder, thus concentrated, receives a
large additional supply of solid matter through the agency of the green
cells of the leafy parts, which take in carbon from the atmosphere
(§ 83) ; so that it now includes a considerable amount of gummy
matter, in the state prepared for being converted into solid tissue ; as
well as numerous other compounds. Now this elaborated sap is then
conveyed into the various parts of the system, through the agency of
a network of vessels, which takes its origin in the leaves, and extends
along the branches to the stem and roots, chiefly in the bark of those
parts. These vessels are strictly analogous to the capillaries or small-
est blood-vessels of Animals ; but they differ from them in this, —
that the capillary network of Animals communicates on either side
with larger trunks, being formed, in fact, by the interlacement or
anastomosis of their minutest branches, — whilst the network of nutri-

316 CIRCULATION OF ELABORATED SAP.

live vessels in Plants is everywhere continuous with itself, not having
any communication with large vessels, so that the fluid prepared in
the leaves commences a circulation there, which is continued on the
same plan, until it has found its way to its remote destination in the
roots.

544. The natural movement of the elaborated sap through these
vessels may be studied, under favourable circumstances, with the
assistance of the microscope ; the requisite conditions being, that the
part should be sufficiently transparent for the vessels to be distinctly
seen, that the sap shall contain globules in sufficient number to allow
its movement to be distinguished by their means, and that the circu-
lation should be observed without the separation of the organ exam-
ined from the rest of the Plant, which would produce irregular move-
ments, by the escape of the sap from the wounded part. These
conditions may be attained in many Plants; — most conveniently,
perhaps, in the stipules of the Ficus elastica, one of the trees which
affi^rds the largest supplies of Caoutchouc ; and it is then found that
the movement takes place in the following manner. Distinct currents
are seen, passing along the straightest and most continuous vessels,
and crossing by the lateral connecting branches of the network.
These currents follow no determinate direction; some proceeding up,
and others down ; some to the left, and others to the right : not un-
frequently a complete stoppage is seen in one or more of the channels,
without any obvious obstruction ; and the movement then recom-
mences, perhaps, in the opposite direction. The influence of a force,
developed by the act of circulation, which determines the direction of
the movement, appears from this ; that if a tube be cut off', so as to
give its contents an equally free exit at both ends, the sap only flows
out at one extremity. The movement is retarded by lowering the
temperature of the surrounding air, and it is completely checked by
extreme cold ; it is capable of being renewed by moderate warmth ;
and a further addition of heat increases its rapidity. By a strong
electric shock, the force by which the latex is propelled seems to be
altogether destroyed ; for the movement then ceases entirely.

545. Now it is quite certain that this circulation cannot be due to
any m5 a tergo ; both because it is not constant in its direction in
particular vessels ; and because there is no organ in which any pro-
pelling force, that could extend itself through such a complex system
of vessels, may be developed. Nor can it be in any way due to
the force of gravity ; for although this may assist the descent of the
fluid through the stem, it is totally opposed to its ascent from the ends
of its branches towards their origin, when, as often happens, the
latter are at the higher level. Moreover, it may be noticed that this
circulation takes place most readily, in parts that are undergoing a
rapid development; and that its energy corresponds with the vitality
of the part. Further, it may be observed to continue for some time
in parts that have been completely detached from the rest; and on
which neither vis a tergo, nor vis a fronte, can have any influence.

CIRCULATION OF ELABORATED SAP. 317

It is evident, then, that the force, — whatever be its nature, — by which
this continued movement is kept up, must be developed by the pro-
cesses to which that movement is subservient ; in other words, that
the changes involved in the acts of nutrition and secretion are the
real source of the motor power. The manner in which they become
so, is the next object of our inquiry ; and on this subject, some new
views have recently been put forth by Prof. Draper, which seem to
account well for the phenomena.

546. It is capable of being shown, by experiments on inorganic
bodies, that, if two liquids communicate with each other through a
capillary tube, for the walls of which they both have an affinity, but
this affinity is stronger in the one liquid than in the other, a move-
ment will ensue ; the liquid which has the greatest affinity being
absorbed most energetically into the tube, and driving the other
before it. The same result occurs when the fluid is drawn, not into
a single tube, but into a network of tubes, permeating a solid struc-
ture ; for if this porous structure be previously saturated with the
fluid, for which it has the less degree of attraction, this will be driven
out and replaced by that for which it has the greater affinity, when it
is permitted to absorb this. Now if, in its passage through the porous
solid, the liquid undergoes such a change, that its affinity be dimin-
ished, it is obvious that, according to the principle just explained, it
must be driven out by a fresh supply of the original liquid, and that
thus a continual movement in the same direction would be produced.

547. Now this is precisely that which seems to take place in the
organized tissue, permeated by nutritious fluid. The particles of this
fluid, and the solid matter through which it is distributed, have a cer-
tain affinity for each other ; which is exercised in the nutritive changes,
to which the fluid becomes subservient during the course of its circu-
lation. Certain matters are drawn from it, in one part, for the sup-
port and increase of the woody tissue ; in another part, the secreting
cells demand the materials which are requisite for their growth, — as
starch, oil, resin, &c.; and thus in every part that is traversed by the
vessels, there are certain affinities between the solids and the fluids,
which are continually being newly developed by acts of growth, as
fast as those which previously existed are satisfied or neutralized by
the changes that have already occurred. Thus in the circulation of
the elaborated sap, there is a constant attraction of its particles
towards the walls of the vessels, and a continual series of changes
produced in the fluid, as the result of that attraction. .The fluid,
which has given up to a certain tissue some of its materials, no
longer has the same attraction for that tissue ; and it is consequently
driven from it by the superior attraction, then possessed by the tissue
for another portion of the fluid, which is ready to undergo the same
changes, to be in its turn rejected for a fresh supply. Thus in a
growing part, there is a constantly renewed attraction for the nutritive
fluid, which has not yet traversed it ; whilst, on the other hand, there
is a diminished attraction for the fluid, which has yielded up the nu-

318 CIRCULATION IN PLANTS AND LOWER ANIMALS.

tritive materials required by the particular tissues of the part; and thus
the former is continually driving the latter before it.

548. But the fluid which is thus repelled from one part, may still
be attracted towards another ; because that portion of its contents,
which the latter requires, may not yet have been removed from it.
And in this manner, it w^ould seem, the flow of sap is maintained,
through the whole capillary network, until it is altogether exhausted
of its nutritive matter. The source of the movement is thus entirely
to be looked for in the changes, which take place in the act of growth ;
and the influence of heat, cold, and other agents, upon the movement,
is exercised through their power of accelerating or retarding those
changes. — The fluid which thus descends through the stem and roots,
seems to be at last almost entirely exhausted ; a portion of it appears
to find its way into the ascending current, and to be mingled with
the ascending current; but all the rest seems to have been entirely
appropriated by the different tissues, through which it has circulated.
Thus there is no need of any general receptacle, into which it may be
collected, and from which it may take a fresh departure ; such as is
afforded by the heart of Animals. And as the purpose of this circu-
lation is only to supply the nutritive materials, and not to convey
oxygen, — this element being but little required in the vegetative pro-
cesses, and being supplied by other means, — the same energy and
rapidity are not required in it, as need to be provided for in the higher
Animals.

549. A condition of the Circulating system very similar to this,
exists in several of the lower Animals, as well as in the embryo-state
of the higher. In the very lowest, no blood-vessels are required, for
the same reason that no sap- vessels exist in the lowest Plants ; —
namely, because every part absorbs and assimilates nutritious fluid for
itself, so that it does not require a supply from vessels. As, in the
Sea-Weeds, the whole substance is nourished by direct absorption
from the fluid in contact with the external surface, every part of which
seems endowed with the same absorbent power, so in the Polypes do
we find, that the whole substance is nourished by direct absorption
from the internal surface, w^hich forms the lining of the digestive
cavity. In the same manner, the Aeration of the animal fluids, — or
the exposure of them to the air contained in water, by which they may
part with carbonic acid and imbibe oxygen, — is provided for, not by
any special respiratory organs, but by the contact of water with every
part of the soft external and internal surfaces. Further, as the sub-
stance of their body is nearly of the same kind in every part, they do
not require the continual interchange of the fluid distributed to its
several portions. Thus no circulation is necessary, in these simple
animals, either for the nutrition of their tissues, or for the aeration of
the fluids. The same is the case with others of the lower tribes ; as
well as with the embryo of the higher Animals, at the earliest periods
of their development. Thus the lower Entozoa, or parasitic worms,
have a digestive cavity channeled out, as it were, in their soft gela-

CIRCULATION IN LOWER ANIMALS, AND IN EMBRYO.

319

tinous tissues; and from the walls of this, the nourishment is drawn
by the several component parts of those tissues, without the mediation
of vessels. And the embryo even of Man, in its early condition,
consists of an aggregation of cells, each of which absorbs for itself
from the nutritious fluid with which it is surrounded, and goes through
all its functions independently of the rest.

550. Proceeding a little higher, we find the first appearance of
proper vessels in the higher Entozoa, and in the Mcalephce or Jelly-
fish. These vessels take up the nutritive fluid from the walls of the
digestive cavity, on which they are spread out, just as the roots of
Plants do from the soil. They then unite into trunks, by which the
fluid is conveyed to the more distant parts of the structure, in the
same manner as the ascending sap is conveyed to the leaves by the
vessels of the stem and branches ; and these trunks again subdivide,
and form a network of capillary vessels, which are dispersed through
the several parts of the fabric ; some of them being very abundantly
distributed upon a portion of the surface, which "is particularly destined
to perform the respiratory function. Through these capillary vessels,
the fluid seems to move in very much the same manner, as through
the system of anastomosing vessels in Plants ; — that is, its motion is
due, rather to forces which are developed during its circulation, than
to any vis a tergo derived from the contractile power of a propelling
organ. But there is this diflference ; that, after having traversed the
minute vessels, and yielded up to the tissues a part of the solid matter
which it contains, the fluid is collected again by other trunks, which
convey it back to the point from
which it started ; there it is min-
gled with the fluid that has been
newly absorbed, and with that
which has undergone aeration ;
and it is then distributed, as be-
fore, through the general capil-
lary network of the body.

551. Now this is very much
the condition of the human em-
bryo, at the time when vessels
are first developed in its sub-
stance. These vessels are form-
ed by the coalescence of cells;
and from the contents of these
cells, which have been imbibed
from the yelk, the first blood
seems to be derived. The first
formation of blood-vessels takes
place, not in that part of the em-
bryonic structure which is to be
developed into the perfect animal, but in a membranous expansion
from it, which surrounds the yelk, and which answers the purpose of

Vascular Area of Fowl's egg, at the beginning of
the third day of incubation ;— a, a, yelk; b, b, b, b,
venous sinus bounding the area: c, aorta; d, punc-
tum saliens, or incipient heart; e, e, area pellucida;
/,/, arteries of the vascular area; g-jg, veins; A, eye.

320 CIRCULATION IN LOWER ANIMALS.

a temporary stomach. A capillary network is formed in a limited
portion of this membrane, termed the vascular area (Fig. 83) ; and
this not by the branching of larger trunks, these trunks being subse-
quently formed by the reunion of the capillaries. The first movement
of the blood is towards the central spot, in which the organs of the
permanent structure are being evolved ; and it takes place before the
incipient heart has acquired any muscularity, so that it must be quite
independent of any contractile force exerted by that organ. Here
too, then, we perceive that the circulation is essentially capillary ; and
that it is sustained by forces very different from those, of which the
action is most evident to us in the higher animals.

552. As we ascend the animal scale, however, we find that pro-
vision is made for a more regular and vigorous Circulation of the
Blood, than that which exists in the lowest classes. Thus in the
class of Echinodermata (including the Star-fish and Sea-Urchin), a
portion of the principal vessel is peculiarly endowed with contractile
power; and this may be seen in constant pulsation, like the heart of
the higher animals, — alternately contracting, to propel the fluid it
contains, through the vessels that issue from it, — and then dilating,
to receive a fresh supply from the vessels that pour their contents
into it. A similar provision is observable in the lower tribes of
Worms, in which this contractile vessel lies along the back ; pro-
pelling the blood forwards, by a sort of peristaltic movement, through
trunks which pass out at its anterior termination ; and receiving it
again, after it has circulated through the system, by vessels which
enter at its posterior extremity. In the higher orders of Worms, in
the Myriapoda or Centipede tribe, and in Insects, we find this dorsal
vessel divided by transverse partitions containing valves, into separate
cavities which answer to the different segments of the body. Each
of these is, to a certain extent, the heart of its own segment, receiving
and propelling blood by trunks which open into it ; but they all par-
ticipate in the more general circulation just described, a large portion
of the blood being poured into the hindermost segment, transmitted
forwards from cavity to cavity through the valves which separate
them, and at last propelled through trunks that issue from the most
anterior segment. In some instances we find that two or three of
these trunks, on either side, pass round the oesophagus, and reunite
below it, so as to enclose it in a sort of collar ; and they form a main
trunk by this union, which runs backwards along the under surface of
the body, and which distributes the blood to its different organs by
lateral branches. These subdivide into a capillary network ; and the
returning vessels, w^hich originate in this network, pour the blood
which has circulated through it into the posterior cavity of the dorsal
vessel. — Still it is very evident, from the observation of the circulation
in those transparent species, in which the whole process can be dis-
tinctly watched under the Microscope, that the contractile power of
the dorsal vessel is far from sufficient of itself to sustain the Circula-
tion ; and that the movement of the blood through the capillary net-

CIRCULATION IN ARTICULATED CLASSES. 321

work is in part due to forces developed during its progress, — being
often retarded or accelerated in particular spots, without any visible
change in the propelling force of the central organ.

553. In most of these animals, there are distinct organs of Respi-
ration, confined to some one part of the body ; and we often find that
the vessels which convey blood to them, are furnished with distinct
contractile portions, like so many supplementary hearts, for the pur-
pose of propelling the blood through thera more energetically. In
proportion as we ascend the series of Articulated animals, do we find,
for the most part, a more vigorous and regular circulation, both for
the nutrition of the system, and for the transmission of the blood
through the respiratory organs ; but there is an exception in the case
of Insects, which deserves special notice. In this class, the circula-
tion is much less vigorous than it is in other Articulated animals of
similar complexity of structure ; though it might have been antici-
pated, that the extraordinary activity of their movements would ne-
cessitate a corresponding rapidity in the circulating current, espe-
cially for the purpose of conveying an extraordinary supply of oxygen
to the nervous and muscular systems. But this is provided for in
another way ; the air being conveyed to these tissues, not through
the blood, but by direct transmission through the minute ramifications
of the air-tubes or tracheae, which penetrate the very smallest organs of
the body.

554. The condition of the Circulating apparatus in the Embryo of
higher animals, at a period a little advanced beyond that just alluded
to, presents a striking analogy with that last described ; for the heart,
at the time of its first formation, seems like a mere dilatation of the
principal vascular trunk, having thickened walls, in which, after a
time, muscular fibre begins to be developed, and the contractile power
manifests itself. The pulsation of this heart, how^ever, does not
seem to extend its influence immediately through the vascular area-;,
the capillary circulation in which, remains for some time in great
degree independent of it. There is no resemblance in form^ how-
ever, between the dorsal vessel of Insects, and the incipient heart of
the higher animals ; since the latter is never much prolonged, and
speedily becomes doubled (as it were) upon itself; and its first division
into distinct cavities is merely for the purpose of separating its receive
ing portion, or auricle, from its propelling portion, or ventricle. But the
general condition of the Circulating system is much the same in the
two cases ; and it is further alike in this, — that it is not always easy
to show that the vessels have distinct walls, as they frequently seem-
like mere channels excavated in the tissues.

555. We may next turn our attention briefly to the condition of
the Circulating apparatus in the Molluscous classes, which has lately
been found to present some very peculiar characters. In these it
would seem as if the moving power were more concentrated in the
heart, than in the preceding; for this organ seems no longer like a
mere dilatation of the vascular trunk, but is a distinct sac with musr

21

822 CIRCULATION IN MOLLUSKS.

cular walls, usually having at least two cavities, an auricle and a ven-
tricle. The usual course of the circulation is the following. The
blood, expelled from the ventricle of the heart, passes along the main
systemic artery, or aorta ; which distributes it to the body at large.
It is then collected again, and transmitted to the respiratory organs ;
in which it is exposed, either to the air contained in the surrounding
water, or (in the terrestrial Mollusks) more directly to the atmosphere ;
and from these it is returned to the heart, to be again transmitted to
the system. Thus we see that the heart of these animals receives
and impels aerated blood ; and that its office is to send that blood to
the capillaries of the general system. Hence it may be called a 5^5-
temic heart.

556. The blood, in the first part of its course, passes through dis-
tinct vessels : it has been lately shown, however, that in the Mollusks
in general, the blood which has passed through the systemic capilla-
ries, and is on its way to the respiratory organs, is no longer thus
confined, but that it meanders through passages or sinuses, which are
channeled out in the tissues, and which even communicate freely with
the abdominal cavity in which the viscera lie ; so that their whole
exterior is bathed by the circulating fluid. It is perhaps in this part
of its course, that it most readily takes up the fresh nutrient mate-
rials, which have been prepared by the digestive process, and which
would, under such circumstances, find their way with comparative
facility from the inner surface of their walls to the outer. — After being
thus diffused, in its venous or carbonized state, through the substance
of the tissues and through the visceral cavity, it is again collected
into distinct trunks ; and these convey it to the respiratory organs. —
Now although it cannot be doubted, that the impelling power of the
iheart is the chief cause of the movement of the blood through the sys-
temic vessels, yet it would seem impossible to suppose, that this
power can be exerted over the unrestrained currents, in which it is
diflfused through the body, after passing through the systemic capil-
laries ; and it can scarcely be doubted, that its passage through the
capillaries of the respiratory organs is due to the power which is
'developed in themselves, under the conditions already alluded to.

557. There is a very curious phenomenon to be observed in the
•circulation of some of the lowest Mollusks; namely, the continual
.reversal of the course of the current. The heart, in these animals, is
«nuch less perfectly formed, than in the higher tribes; and seems
anore like the mere contractile dilatation of the principal trunk, which
is the sole representative of that organ in the Echinodermata. The
circulating fluid is sometimes transmitted first to the system ; and,
after being distributed to its different parts by the ramifications of the
main artery, it meanders through the channels excavated in its tis-
sues ; and then flows towards the respiratory surface, after passing
over which, it returns to the heart. But after a certain duration of
its flow in this direction, the current stops, and then recommences in
the contrary direction, — proceeding first to the respiratory organs, and

CIRCULATION IN FISHES.

323

Fig. 84.

then to the system in general. It would seem as if in this, one of the
lowest forms of animals possessing a distinct Circulation, the central
power were not yet sufficiently strong, to determine the course which
the fluid is to take ; so that it undergoes continual vacillations. In a
group of Compound Polypes, to which this class of Mollusks has
many points of affinity, there is a movement of fluid through the stem
and branches, which in like manner continually changes its direction.
This movement, however, can scarcely be regarded in the light of a
proper Circulation ; since the tubes in which it occurs are in direct
communication with the digestive cavities of the Polypes. But the
flow seems altogether independent of any mechanical propulsion ;
and takes place most energetically and regularly towards parts in
which new growth is going on.

558. We have now to consider the chief forms in which the Cir-
culating apparatus presents itself in the Vertebrated classes ; and first
in that of Fishes. We have here, as in Mollusks, a heart with two
cavities, an auricle and a ventricle ; this heart, however, is not placed
at the commencement of the systemic circulation, but at the origin of
the respiratory vessels. The blood which it receives and propels, is
venous or carbonized ; this is transmitted along a main trunk, which
speedily subdivides into lateral branches or
arches ; and these distribute it to the fringes
of gills, that hang on the sides of the neck.
By the action of the water on the gills, the
blood is aerated in its passage through them ;
and it is then collected by a series of converg-
ing vessels, which reunite to form the great
systemic artery, or aorta. By the ramifica-
tions of this artery, the blood, now aerated, is
distributed through the system, and affords the
requisite nourishment and stimulation to its
tissues. Returning from the systemic capil-
laries in a venous state, the blood of the head
and anterior portion of the body finds its way
at once into the great systemic vein, or vena
cava, by which it is conveyed back to the au-
ricle of the heart ; but that which has traversed
the capillaries of the posterior part of the body,
and of the abdominal viscera, is conveyed by
a distinct system of veins to the liver and the
kidneys. In these organs, the veins again
subdivide into a network of capillaries, which
is distributed through the secreting structure,
and which serves to afford to the secreting
cells the materials.of their development. This
is termed the portal system of vessels. From
the capillaries of the liver and kidneys, the blood is finally collected
by the hepatic and renal veins, which convey it into the vena cava;

Diagram of ihe Circulating
Apparatus of Fishes;— a, the
auricle; &, the ventricle; c,
the trunk supplying the bran-
chial arteries, d, the aerated
blood returning from the gills
is conveyed by e, e, the bran-
chial veins, to /, the aorta,
which distributes it to the sys-
tem; thence it is collected,
and returned to the auricle,
by the veins which unite iu
the vena cava, g.

324 CIRCULATION IN FISHES.— LANCELOT.

where it is mingled with the blood that has not passed through those
organs, and is thus conveyed to the heart.

559. The heart of Fishes, then, belongs to the respiratory circula-
tion. It propels venous blood to the capillaries of the gills, in which
it is aerated ; returning from these, the aerated blood is transmitted
through a second set of capillaries, those of the system, in which it
again becomes venous ; whilst a portion of this blood is made to tra-
verse a third set of capillaries, those of the liver and kidneys, before
it is again subjected to the propelling power of the heart. Now as
the heart, instead of being stronger than it is in animals with the com-
plete double circulation presently to be described, — in which the
greater part of the blood propelled by it only traverses one set of
capillaries, and never more than two, — is much weaker in proportion,
it is evident that here, too, a supplementary power must exist, by
which the flow of blood through the capillaries is aided, and on which,
indeed, the portal circulation must greatly depend.

560. It is requisite that, in the class of Fishes, the whole of the
venous blood returned from the system should pass through the respi-
ratory organs before being again transmitted to the body ; since the
aerating action of the small quantity of air diffused through the water,
w^ould otherwise be insufficient for its renovation. But in Reptiles,
all of which breathe air during their adult condition, the case is very
different ; for if the whole current of their blood were exposed to the
atmosphere, before being again sent to the body, the quantity of oxy-
gen conveyed into the tissues w^ould be too great, and would have
an over-stimulating effect. The plan of the Circulation is, therefore,
differently arranged in Reptiles. We find the heart to consist of three
cavities ; two auricles and one ventricle. From the ventricle issues
a single trunk, which speedily subdivides; some of its branches pro-
ceeding to the lungs, and others to the body. The blood which is
transmitted through this trunk, is of a mixed character, as we shall
presently see ; being neither fully aerated, nor yet highly carbonized.
It contains sufficient oxygen, to stimulate the nervous and muscular
systems of these comparatively inert animals ; whilst it also contains
enough of carbonic acid, to require being exposed to the atmosphere
through the medium of the lungs. The blood which has passed
through the systemic capillaries, and which has been thereby ren-
dered completely venous, is returned to one of the auricles — the
systemic — by the vena cava. On the other hand, the blood which
has passed through the capillaries of the lungs, and which has
been thereby rendered completely arterial, is returned through the
pulmonary vein to the other auricle, — the pulmonary. Thus one
of the auricles exclusively receives aerated, and the other carbonated
blood ; and as both pour their contents into the common ventricle,
the blood which that cavity contains and propels ;s of a mixed cha-
racter.

561. An extremely interesting aspect of the circulating apparatus
is presented by the Amphioxus or Lancelot ; an animal which presents

I

CIRCULATION IN REPTILES. 325

the general form of a Fish, and which can scarcely be referred to any-
other group ; but in which the characters of the Vertebrated series are
degraded (as it were) to the level of the lowest Molluscous and Ver-
miform classes. The blood, which is white, moves through distinct
vessels, but there is no proper heart ; and the vascular trunks present
several dilatations, in different parts, which have muscular walls,
and show contractile power. Thus the circulation is carried on, not
through the agency of a central impelling organ, as in Fishes ; but
by power which is scattered or diffused through various parts of the
system of blood-vessels, as in the lower Invertebrata. — The respira-
tory apparatus, also, is formed upon a type much lower than that of
Fishes ; for it consists simply of a dilatation of the first part of the
alimentary canal, or pharynx, upon the walls of which the blood is
distributed in divided streams, its cavity being filled with water,
which serves to aerate the blood. This is precisely the type, on
which the respiration is eflfected, in those lowest Mollusks, of which
mention has just been made, as exhibiting alternations in the direction
of the circulating current (§ 557). In other respects, however, the
arrangement of the vascular system in this extraordinary animal, cor-
responds with that which obtains in Fishes.

562. Various modifications of this form of Circulating apparatus
exist in the different groups of Reptiles. In the lowest among them,
which breathe permanently by gills like Fishes, besides possessing
imperfectly developed lungs, the apparatus exhibits a blending of
both plans; for a small portion of the blood, which is propelled by
each contraction of the ventricle, passes directly to the lungs; the
principal part of it being at once distributed to the gills as in Fishes.
After passing through these, it is transmitted to the general system ;
and on returning thence, in a completely venous state, it is mingled
with the blood which has been arterialized in the lungs. This latter,
however, bears so small a proportion to the rest, that, if the aeration
were not partly effected by the gills, it would be insufficient for the
wants of the animal. — The tadpoles of the common Frog and Water
Newt, as well as of other species which, like them, begin life in the
general condition of Fish, present a similar condition at one period
of their change. At first, the whole aeration is effected by means of
gills, the lungs being in a rudimentary or undeveloped state ; and the
entire circulation is carried on as in Fishes, the pulmonary vessels
being scarcely traceable. As the lungs begin to be developed, how-
ever, a portion of the blood is sent to them ; and at the same time,
communicating passages which previously existed, between the ves-
sels that convey blood to the gills, and those that return it from them,
are increased in size ; so that a certain proportion of the blood is trans-
mitted to the system, without having passed through the gills at all.
By a further increase in the diameter of these, the whole current of
blood takes this direction, the gills being no longer serviceable ; and
as, at the same time, the lungs are attaining their full development,
the aeration which they effect in the blood transmitted to them be-

326

CIRCULATION IN MAMMALS.

Fig. 85.

comes sufficient, and the whole circulation is thus permanently estab-
lished on the Reptile type.

563. On the other hand, among the
higher Reptiles, we find the circulating ap-
paratus presenting approaches to the form
it possesses in Birds and Mammals. For
the ventricle is divided, more or less com-
pletely, into two cavities, one of which
propels aerated blood to the system, whilst
the other transmits venous blood to the
lungs. A certain amount of mixture of
arterial and venous blood always takes
place, however, either in the heart itself,
or in the vessels ; so that the blood which
the body receives is never purely arterial.
But this mixture is sometimes effected in
such a manner, that pure arterial blood is
sent to the head and anterior extremities ;
though the remainder of the body receives
a half-aerated fluid. This is accomplished
in the Crocodile, by a provision very simi-
lar to that which exists in the foetus of
warm-blooded animals (Chap. XI). The
portal circulation in Reptiles is carried on
nearly upon the same plan as in Fishes. It
receives the blood from the posterior ex-
tremities and from the tail, as well as from the abdominal viscera ;
and this blood is distributed by the portal capillaries, not only through
the liver, but also through the kidneys, although the latter also receive
arterial branches from the aorta. The fact that the kidneys are sup-
plied from the general portal circulation, in Fishes and Reptiles, has
an important bearing on the difference in the arrangement of their
own vessels, which will be hereafter shown to exist, between the kid-
neys of these animals, and those of Birds and Mammals (§ 727).

564. In the warm-blooded division of the Vertebrated series, which
includes the classes of Birds and Mammals, we find the whole circu-
lation possessed of a greatly increased energy ; but the distinguishing
peculiarity of the apparatus in these animals, is that conformation of
the heart and vessels, which secures a complete double circulation of
the blood ;— that is, which provides for the aeration of every particle
of the venous blood which has returned from the system, before it is
again sent into the tissues. The heart may be regarded as consisting
of two distinct parts, — a systemic heart, like that of the MoUusks,
forming its left side, — and a respiratory heart, like that of Fishes,
constituting its right. Each of these parts has a receiving cavity or
auricle, and an impelling cavity or ventricle. The cavities of the
two sides are completely separated from one another, in the adult
state at least ; though their walls are united, for economy of material.

Diagram of the Circulation in
Reptiles : — a, single ventricle, re-
ceiving the aerated blood from 6,
the pulmonary auricle, and venous
blood from c, the systemic auricle;
and propelling part of this mixed
fluid to the pulmonary capillaries
d, and part to the systemic capil-
laries, e.

CIRCULATION IN MAMMALS.

327

Fig. 86.

It is obvious that much is saved in this manner ; since, as the con
tractions of the auricles and of the ven-
tricles on the two sides occur simultane-
ously, the pressure of blood in the one is
partly antagonized by that on the other,
wherever it acts on the wall that is com-
mon to both. This antagonism is not
complete, however ; since the systemic
ventricle contracts with far greater force
than the pulmonary ; and the wall be-
tween them must be capable of resisting
the difference of pressure on its two
sides thus occasioned. — The blood which
is returned from the system, in a venous
state, through the vena cava to the right
auricle, and which is poured by it into
the right ventricle, is impelled by the
latter through the capillaries of the lungs,
where it undergoes aeration. Returning
thence, in an arterialized state, it is con-
veyed into the left auricle, and thence
flows into the left ventricle ; by which it
is propelled through the great systemic
artery or aorta, and through its ramifica-
tions to the general system.

565. The greater part of the blood,
which has been rendered venous by pas-
sing through the systemic capillaries,is col-
lected bythe systemic veins, and is returned directly to the heart through
the vena cava. But a portion is still employed for the distinct circula-
tion, which is destined to supply the materials for the secreting action
of the liver. The blood that has traversed the capillaries of the walls
of the alimentary canal, and of the other viscera concerned in diges-
tion, is collected again by the converging veins into a large venous
trunk, the vena portee, by which it is distributed through the liver.
This vessel, although formed by the convergence of veins, and con-
veying venous blood, has really the character of an artery in an equal
degree ; for it subdivides and ramifies after its entrance into the liver,
so as to form a network of capillaries, from which the blood is again
collected, and thence transmitted by the hepatic vein to the vena cava.
— Thus that portion of blood, which supplies the liver with the mate-
rials of its secreting action, passes through two sets of capillaries,
between the time of its leaving the heart and its return to it. The
portal circulation in Birds, as in Reptiles and Fishes, receives the
blood from the posterior part of the body, and from the extremities ;
but the portal blood is only conveyed to the liver; the kidneys being
supplied by the renal arterv.

Diagram of the Circulating Ap-
paratus in Mammals and Birds : — a,
the heart containing four cavities ; b,
vena cava, delivering venous blooa
into c, the right auricle ; d, the right
ventricle, propelling venous blood
through e, the pulmonary artery, to/,
the capillaries of the lungs ; g, the
left auricle, receiving the agrated
blood from the pulmonary vein, and
delivering it to the left ventricle, h,
which propels it through the aorta i, to
the systemic capillaries, j, whence
It is collected by the veins, and car-
ried back to the heart through the
vena cava, b.

328

CIRCULATION IN MAMMALS. ^

Fig. 87.

Anatomy of the human heart and lungs. 1. The right ventricle ; the vessels to the right of the
figure are the middle coronary artery and veins ; and those to its left, the anterior coronary artery and
veins. 2. The left ventricle. 3. The right auricle. 4. The left auricle. 5. The pulmonary artery.
6. The right pulmonary artery. 7. The left pulmonary artery. 8. The remains of the ductus arte-
riosus 9. The arch of the aorta. 10. The superior vena cava. 11. The right arteria innominata,
and in front of it the vena innominata. 12. The right subclavian vein, and behind it its corresponding
artery. 13. The right common carotid artery and vein. 14 The left vena innominata. 1.5. The left
carotid artery and vein. 16 The left subclavian vein and artery. 17. The trachea. 15. The right
bronchus. 19. The left bronchus. 20,20. The pulmonary veins; 18,20, form the root of the right
lung; and, 7, 19. 20, the root of the left. 21. The superior lobe of the right lung. 22. Its middle lobe.
23. Its inferior lobe. 24. The superior lobe of the left lung. 25. Its inferior lobe.

566. This perfect form of the Circulating apparatus is only attained,
in the warm-blood animal, after a series of transformations, which
strongly remind us of the permanent forms presented by the vascular
system in Fishes and Reptiles. Thus in the embryo of the Chick at
about the 60th hour, and in that of the Dog at about the 21st day,
the curved and dilated tube, of which the heart previously consisted,
(§ 554,) is found to be distinctly divided into an auricle and a ven-
tricle. From the latter originates the main arterial trunk, which
divides into four pairs of lateral branches; and these pass round the
pharynx precisely in the position and direction of the arteries of the
gills of Fishes. They do not, however, distribute the blood to gill-
tufts; for none such are developed in the embryo of the warm-blooded
ainimal; but they meet again below the pharynx, to form a trunk,
•which supplies the general circulation. — Within a short period, how-
ever, the whole plan of the circulation undergoes a change. The
auricle and the ventricle are each divided by a partition, that is de-
veloped in the middle of the heart ; and thus the two auricles and the
two ventricles are formed. Whilst this is going on, a change takes
place also in the vessels that arise from the heart; for the arterial
trunk, that was previously single, undergoes a division into two dis-
tinct tubes; one of which is connected with the left ventricle, and

MOVING POWERS OF THE CIRCULATION. 329

becomes the aorta, whilst the other originates in the right ventricle,
and becomes the pulmonary artery. Of the four pairs of branchial
arches, some are subsequently obliterated ; whilst others undergo
changes that end in their becoming the arch of the aorta, the right
and left pulmonary arteries, and the right and left subclavians.

567. The muscular power of the heart is much greater in the warm-
blooded than in the cold-blooded Vertebrata, in proportion to the
extent of the circulation which it is concerned in maintaining ; and
it is evidently destined to take a much larger share in the propulsion
of the fluid, than it is in the lower tribes. Many Physiologists, indeed,
are of opinion that the movement of the blood is entirely due to the
action of the heart; and this view appears to be supported by the
results of numerous experiments upon the circulation. But it is very
difficult, if not impossible, to make experiments that shall be really
satisfactory upon this point ; and it appears safer to trust to the " expe-
riments ready prepared for us by Nature," as Cuvier termed them, —
namely, those lower forms of animated being, in which various diver-
sities of structure present themselves, and in which we can study the
regular and undisturbed effects of these. — Thus we have seen that,
in Plants and the lowest Animals, which have no central impelling
cavity, the movement of the nutritive fluid is entirely dependent upon
the power that is diffused through the network of vessels in which it
circulates. As we ascend the series, we find an organ of impulsion
developed upon a certain part of the vascular system, whose object
it is to give increased energy and regularity to the movement. And
ascending still higher, we find the moving power gradually con-
centrated, as it were, in this organ ; yet it is not altogether with-
drawn from the capillary network, as we shall see from several facts
to be presently adduced. The particular actions of the Heart, the
Arteries, the Capillaries, and the Veins, will now be considered in
more detail.

3. Action of the Heart,

568. The Heart is a hollow muscle, endowed in an eminent degree
with the property of irritability ; by which is meant, the capability of
being easily excited to movements of contraction alternating with re-
laxation (§ 347). At first sight, its actions seem different from that
of the muscles, which are called into action by the impulse of the will ;
for in these there is apparently no such alternation, the state of con-
traction being kept up as long as the will operates. But it has been
already explained that, even in these, the individual fibres are proba-
bly in a state of continual alternation of contraction and relaxation,
during their active condition, — one set taking up the action, whilst
another is returning to the state of relaxation. Hence the chief pecu-
liarity in the Heart's action consists in this, — that the whole mass of
fibres of each division of the organ contract and relax together. The
contraction of the two ventricles is perfectly synchronous, as is that of

330 MOVEMENTS OF THE HEART.

the two auricles ; but the contraction of the auricles is synchronous
•with the dilatation of the ventricles, and vice versa. The regularity
of this alternation, however, is somewhat disturbed, when the irrita-
bility of the heart is becoming exhausted ; and both sets of movements
will continue, when the auricle and ventricle have been separated
from one another. Their regular succession, in the natural state, is
doubtless in part due to the fact, that the transmission of blood from
the auricle into the ventricle, by the contraction of the former, is the
stimulus which most effectually excites the latter to contraction ; whilst
the ventricle is contracting, the auricle, now free to dilate, is distended
by the flow of blood from the veins that open into it ; and this flow
stimulates it to renewed contraction, just at the time when the con-
traction of the ventricle has been completed, and its state of relaxa-
tion enables it to receive the blood poured in through the orifice lead-
ing from the auricles.

569. In the living animal, the auricular and ventricular movements
succeed one another with great regularity ; and when the circulation
is proceeding with vigour, scarcely any appreciable pause can be dis-
covered between the different acts. The contraction or systole of the
Auricle takes place precisely at the same moment w^th the dilatation
or diastole of the Ventricles; and, as soon as the latter are full, and
the former are empty, the diastole of the Auricles, and the systole of
the Ventricles, immediately succeed. The systole of the Ventricles
occasions the propulsion of blood into the arterial system ; and this
action produces the pulse, as will be explained hereafter. And it also
corresponds with the impulse or stroke of the heart against the parietes
of the chest. This impulse is not produced, as some have supposed,
by the swinging of the entire heart forwards ; but by the peculiar
mode in which the Ventricular systole takes place. In the contraction
of its walls, every dimension is lessened ; but shortening is the most
perceptible change, the vertical diameter of the Ventricle being the
greatest. Owing to the peculiar spiral disposition of the fibres of the
heart, its apex is not simply drawn upwards by their contraction, but
it is made to describe a spiral movement, from right to left, and from
behind forwards ; and it is in this manner, that it is caused to strike
against the side of the chest.

570. The systole of the Ventricles is immediately followed by their
diastole ; but the commencement of this has been observed to occur
at a small interval previous to the contraction of the Auricles ; and
sometimes a brief interval of repose may be noticed, separating the

Jirst stage of the Ventricular diastole, which may be partily due to the
simple elasticity of the walls of the Ventricles, from the second, which
is accompanied by the systole of the Auricles, and in which the blood
of the latter is forcibly propelled into them. When the circulation is
being carried on regularly, the blood is propelled into the Ventricles
with sufficient force to dilate them strongly ; so that the hand closed
upon the heart is opened with violence. Even the auricles dilate
with more force than it seems easy to account for by the vis a tergo

MOVEMENTS AND SOUNDS OF THE HEART. 331

of the blood in the venous system ; which is small compared with
that which the fluid possesses in the arteries.

571. The natural movements of the Heart are accompanied by cer-
tain sounds, which are heard when the ear is applied over the cardiac
region ; and an acquaintance with these sounds and with their causes
is of much importance, since the alterations which they undergo in
disease, afford us some of our most accurate information in regard to
the nature of the morbid affection. Concurrently with the impulse of
the heart against the chest, a dull and prolonged sound is heard ; this,
which is termed the Jirst sound, marks the ventricular systole, and is
synchronous with the pulsation in the arteries. The second sound,
which is short and sharp, follows immediately upon the conclusion of
the first; and it must therefore be produced during the first stage of
the Ventricular diastole, before the systole of the Auricles has com-
menced. It is followed by a brief interval of repose, which occurs
during the remainder of the Ventricular diastole and the Auricular
systole ; and this is succeeded by a recurrence of the first sound. If
the whole period between two successive pulsations be divided into
four parts, it is estimated that the first sound usually occupies two of
these ; and the second sound, and the interval, one part each.

572. Now in order to understand the causes of these sounds, it is
necessary to study the course of the blood through the heart a little
more in detail. When the Ventricles, distended with blood, are con-
tracting upon their contents, they eject them forcibly through the nar-
row orifices of the aorta and pulmonary artery; and the semilunar
valves, which guard these orifices, are thrown back against the walls
of the arteries. The regurgitation of the blood into the auricles is
prevented by the action of the mitral and tricuspid valves ; but the
flaps of these do not suddenly fall against each other, when the blood
first begins to press them together ; being restrained by the chorda
tendinece. The connection of these with the carnecu columncB, which
form part of the ventricular walls, and contract simultaneously with
them, appears to have this use : — that the flaps of the valves, which
are completely thrown back during the preceding rush of blood from
the auricles to the ventricles, may be drawn into a favourable posi-
tion, for the blood to get behind them and bring them together, so as
completely to close the orifice. As soon as the ventricular diastole
begins to take place (even before the contraction of the auricles has
commenced) there will be a tendency of the blood, that has just been
propelled into the aorta and pulmonary artery, to flow back to the
heart ; but this regurgitation is completely prevented by the semilu-
nar valves of these orifices, which are immediately filled out by this
backward tendency of the blood, and which meet in such a manner
as completely to close the orifices. This closure is much more sudden
than that of the mitral and tricuspid valves, being altogether unre-
strained.

573. The^rs^ sound is certainly in part due to the impulse of the
heart against the thoracic parietes ; as is proved by the fact, that when

332 SOUNDS OF THE HEART.

the impulse is prevented, the sound is much diminished in intensity ;
and also by the circumstance, that, when the ventricles contract with
vigour, the greatest intensity of the sound is over the point of percus-
sion. But that it is not entirely due to this cause, is also sufficiently
evident from two circumstances ; — its prolonged character, which
could scarcely be given by a momentary impulse ; — and its continu-
ance, though with diminished intensity, when the parietes of the
chest are wanting, and even after the complete removal of the heart
from the body. Moreover, the duration of the first sound is much
increased by any morbid state of the orifices of the ventricles, which
obstructs the exit of the blood. Much discussion has taken place as
to the cause of that part of it, which is not due to the impulse ; some
having attributed it to the muscular contraction of the walls of the
ventricles, others to the flow of blood over the irregular surfaces of
their interior, and others to the rush of the fluid through the narrow
orifices leading to the aorta and pulmonary artery. There can be little
doubt, that the first and last of these causes are both concerned in
producing the sound. For as a sound may be distinctly heard by
means of the stethoscope, when the heart is contracting vigorously
out of the body, and when no blood is propelled by it, nothing else
than muscular contraction can be then regarded as its source ; and
there is other evidence that sound may be produced by this cause,
since the vigorous contraction of any other large muscle gives rise to
a continued tingling, which may be heard through the stethoscope.
But when the heart is contracting in its natural position, and is pro-
pelling the blood with its ordinary vigour, the sound is heard in its
greatest intensity at the base of the heart, i.e., at the origin of the
great arteries ; and since any obstruction to the exit of the blood
through them increases the intensity, as well as the length of the
sound, it can scarcely be doubted that it is partly due to the rush of
the blood through the contracted entrances of these vessels. A very
similar sound, known as the " bruit de soufflet," or bellows-sound,
may be heard through the stethoscope, over any large artery, when it
is compressed, so as to permit the passage of blood less readily than
usual. Thus the ordinary first sound may be regarded as composite
in its nature ; being made up of the sound produced by the impulse
of the heart against the parietes of the chest, of the muscular sound
occasioned by the forcible contraction of the thick walls of the ven-
tricles, and of the sound generated by the friction of the particles of
blood against each other, and against the boundaries of the narrowing
orifices which lead into the vessels.

574. The cause of the second sound is simpler, and more easily
understood. It is due to the sudden filling-out of the semilunar valves
with blood, ^t the moment when the ventricular systole has ceased,
and when the commencing diastole produces a tendency to the regur-
gitation of blood from the aorta and pulmonary artery. The sudden
passage of the valves, from a state of complete relaxation to one of
complete tension, occasions a sort of c/icA:; which is the second sound

SOUNDS OF THE HEART— THICKNESS OF ITS WALLS. 333

of the heart. That this is the real cause, has now been fully demon-
strated. If one of the valves be hooked back against the side of the
artery, by the introduction of a curved needle, so that a reflux of
blood is permitted, the sound is entirely suppressed. And if the
complete closure of the valves be prevented by disease, so that their
tension is diminished, and a certain amount of regurgitation takes
place, the second sound is no longer heard in its proper intensity;
whilst, on the other hand, a sound analogous to the first, and some-
times prolonged over the whole interval of repose, indicates the reflux
of the blood into the ventricles. When the semilunar valves are
thickened by morbid deposit, their surface roughened, and their open-
ing narrowed, the first sound becomes harsher and sharper; and the
second sound acquires the same character, — the backward as well as
the forward flow of the blood being affected by this cause.

575. The natural movements of the mitral and tricuspid valves ap-
pear to be accomplished with perfect freedom from sound ; for the size
of the orifices which they guard prevents any considerable friction of
the blood, in its flow from one cavity to the other; and their closure,
when the ventricular systole begins, does not take place with the
rapidity and suddenness of that of the semilunar valves. But w^hen
their structure is changed by disease, their action is not so noiseless;
and they give rise to various morbid sounds, which are heard in addi-
tion to the ordinary sounds, and which may even obscure them alto-
gether— In the same manner the ordinary movements of the heart do
not produce any audible friction sound, between the two surfaces of
the pericardium, that which covers the heart and that which lines the
pericardial sac. These surfaces are kept moist, in health, by the serous
fluid constantly exhaling from them ; and they are extremely smooth ;
so that they glide over one another noiselessly. But if they become
dry, as in the first stage of inflammation, a slight creaking is heard,
accompanying both the ordinary sounds of the heart, and somewhat
resembling the rustling of paper. And if they are roughened by the
deposit of inflammatory exudations, this ** to and fro" sound becomes
of a harsher character.

576. The walls of the left Ventricle are considerably thicker than
those of the right ; and the contractile power is greater. This diflfer-
ence is obviously required, by the diflference in length between the
systemic and the pulmonary vessels; the amount of force necessary to
drive the blood through the latter being far inferior to that which is
requisite to propel it through the former. The average thickness of the
walls of the left Ventricle is about A\ lines; being somewhat greater
than this at the middle of the heart, and less at its apex. The average
thickness of the walls of the right ventricle is not more than 1 J line ;
being a little greater than this at the base, and less at the apex of the
heart. The left auricle is somewhat thicker than the right. — The ca-
pacities of all the four cavities are nearly equal; each of them, in the
full-sized heart, holding about two ounces of fluid. The Ventricles
are, perhaps, a little larger than their respective Auricles; but there

334 RATE OF CIRCULATION.

is no very positive difference in capacity, between the Ventricles and
Auricles of the two sides.

577. The quantity of blood which is propelled at each Ventricular
systole, cannot, therefore, exceed two ounces; and it is probably
somewhat less, as the ventricles do not seem to empty themselves
completely at each contraction. Now the whole quantity of the blood
seems to be about one-fifth of the entire weight of the body ; so that
it will amount to about 28 lbs. in an individual of 140 lbs. weight.
Allowing 75 pulsations to a minute, 150 ozs. (or 91bs. 6 ozs.) of
blood would pass through each ventricle of the heart in that time ;
consequently nearly three minutes would be required for the passage
of the entire mass of the blood through the whole circle of its move-
ment, if its rate be entirely determined by the impulses it receives
from this central organ. — But it appears, from various experiments,
that the rate of circulation is much more rapid than this. For if a
solution of any salt easily detectible in the blood, be injected into
one of the large veins near the heart, it may be traced in the arterial
circulation in from 15 to 20 seconds afterwards; during which inter-
val it must have traversed the whole pulmonary system of vessels
and passed through both sides of the heart. And if the salt be one
which acts powerfully on the heart itself, — as is the case with Nitrate
of Baryta or Nitrate of Potass, — this action is manifested almost at
the same moment with the appearance of the salt in the arteries of
other parts ; thus showing that it has been conveyed by the coronary
arteries into the capillaries of the heart itself. The period required
for the transmission of a saline substance from the veins of the upper
part of the body to those of the lower, — which can scarcely be accom-
plished through any more direct channel than the current that returns
to the heart, then passes through the lungs back to the heart again, and
then flows through the systemic arteries and capillaries to the veins, — is
accomplished in little more than 20 seconds, even in an animal so large
as a Horse. It appears, then, that even the vigorous and constant
action of the Heart is not alone sufficient to maintain the circulation
at its ordinary rate ; and we are not justified, therefore, in excluding
those sources of movement in the higher animals, which evidently
exert so important an influence in the lower.

578. The force with which the heart propels the blood is such, that
if a vertical pipe be inserted into the Carotid artery of a horse, the blood
will sometimes rise in it to a height of 10 feet. From comparative
experiments upon other animals, it has been estimated that the- vigor-
ous action of the heart in Man would sustain a column of blood in
his aorta about 7^ feet high ; or, in other words, that the force with
which the heart ordinarily propels the blood through the aorta, is
equal to that which would be generated by the weight of a column of
blood of the same. size, and 7 J feet high; which weight would be
about 4J lbs. But the force which must be exerted by the heart to
sustain such a column, may be shown, upon physical principles, to
be as much greater than this as the area of a plane passing through

CIRCUMSTANCES AFFECTING RATE OF PULSE. 335

the base and apex of the left ventricle is greater than that of the trans-
verse section of the aorta ; and as the proportion of these arese is about
3-1, the real force of the heart may be stated at about 13 lbs.

579. The number of contractions of the heart, in a given time, is
liable to great variations within the limits of health, from several
causes ; the chief of which are diversities of Age and Sex, amount of
Muscular exertion, the condition of the Mind, the state of the Diges-
tive system, and the period of the Day. — The following are the points
of greatest importance, in regard to the action of these several influ-
ences :

^ge. — The pulse of the newly-born infant averages from 130 to 140
per minute ; and this rate gradually diminishes, until, in adult age, the
pulse averages from 70 to 80 ; and in the decline of life from 50 to 65.

Sex, — The pulse of the adult female exceeds that of the adult male
in frequency, by about 10 or 12 beats in a minute ; and it is also
more liable to disturbance from other causes.

Muscular exertion. — The effect of this in accelerating the pulse is
well known ; but as the amount of change depends upon the degree
of exertion, no general statement can be made on the subject. The
continued influence of a moderate degree of muscular exertion, is
shown by the effect of posture upon the pulse. Thus the pulse is on
the average from 7 to 10 beats faster (per minute) in the standing
than in the sitting posture ; and 4 or 5 beats faster in the sitting than
in the recumbent posture. This amount of variation is temporarily
increased by the muscular effort required for the change of posture ;
but this soon subsides into the continued rate, which the permanent
maintenance of the new posture involves. There are certain states
of the system, in which the heart's action is increased to a most vio-
lent degree, by a simple change of posture; and in which, therefore,
it is necessary that even this slight movement should be made with
gentleness and caution.

Mental Condition. The action of the heart is peculiarly influenced,
as every one is aware, by the excitement of the emotions. This is a
fact to which, however familiar, the medical practitioner should con-
stantly direct his attention. The trifling agitation occasioned by the
entrance of the medical man will produce, in many patients, such an
acceleration of the pulse, as would be very alarming, if its true cause
were not known. And the real rate of the pulse cannot be ascertained,
until time has been permitted for the agitation to subside ; which is
favoured, also, by the influence of a gentle manner and tranquilizing
conversation. The operation of the intellectual powers does not seem
to affect the rate of the heart's movement in any other way, than by
inducing a general state of feverishness, if it be too long or too ener-
getically kept up.

State of the Digestive System. — The pulse is quickened during the
digestion of a meal ; but no exact numerical statement can be made
on this subject.

Period of the Bay. — The frequency of the pulse appears to be some-

336 INFLUENCE OF NERVES UPON HEART'S ACTION.

what greater in the morning than it is in the evening ; and the tem-
porary action of any of the preceding causes more quickly subsides
in the evening than in the morning.

580. The movements of the heart have been supposed to depend
upon a constant supply of nervous influence, generated by the cerebro-
spinal system, and transmitted through the sympathetic nerve, the
branches of which are copiously distributed to it. And this idea
seemed to derive support from the fact, that, when the brain and
spinal cord are removed, or when large portions of the^m are suddenly
destroyed, by crushing or by the breaking up of their substance in any
other mode, the movements of the heart are arrested. But it has
been shown that the brain and spinal cord may h^ gradually removed,
without any such consequence ; and the occasional production of foe-
tuses destitute of those centres, but possessing a regularly-pulsating
heart, is another proof that the movements of this organ do not depend
upon a supply of nervous influence derived from them. Still they are
capable of being influenced by impressions transmitted through the
nerves. It has been ascertained by Valentin, that, after the heart has
ceased to beat, its contractions may be re-excited by stimulating the
roots of the Spinal Accessory nerve, or of the first four Cervical
nerves; the influence of that stimulation being conveyed to the heart
by the Sympathetic system, the cardiac portion of which communicates
with these nerves. Irritation of the Par Vagum, also, has a tendency
to accelerate the heart's action, or to re-excite it when it has ceased ;
but the complete severance of both its trunks produces little disturb-
ance in the regularity of the movement. The action of the heart may
be also affected more directly through the sympathetic system ; thus
it is excited by irritation of the cervical ganglia, especially the first ;
whilst continued pressure upon the cardiac nerve, by an enlarged
bronchial gland, has appeared to be the cause of its occasional sus-
pension. It is without doubt through its nervous connections, and
probably though the sympathetic system, that the heart receives the
influence of mental emotions.

581. The movements of the heart maybe suspended, or altogether
checked, by sudden and violent impressions on the nervous centres,
even though these do not occasion any perceptible breach of substance.
Thus in concussion of the brain, there is not merely insensibility, but
also a complete suspension of the circulation, occasioned by a failure
of the heart's power. This suspension may be permanent, so that
animation cannot be restored ; or it may be temporary, as in ordinary
fainting. The well-known influence of blows upon the epigastrium,
in producing sudden death, is probably to be attributed to a similar
cause, — namely, the shock thus communicated to the extensive plexus
of ganglionic nerves, radiating from the semilunar ganglia, and pro-
ceeding to the abdominal viscera. Violent impressions upon other
nervous expansions may produce a dangerous weakening of the
heart's contractile power ; this is the case, for example, with exten-
sive burns, which may produce faintness, and even death, especially

EQUALIZATION OF FLOW IN THE ARTERIES. 337

in children, by the depression which they induce. Many other causes
of sudden suspension of the heart's action might be enumerated ; but
they may be generally traced to a strong impression upon the nervous
system ; though of the mode in which this operates we know nothing.

4. Movement of the Blood in the Arteries.

582. The Blood, thus propelled from the Heart into the Arteries
by a series of interrupted jets, would continue to flow in the same
manner, if it were not for the equalization of its movement, effected
by the properties of the arterial walls. This influence is exerted by
the middle or fibrous coat, which consists in part of yellow elastic
tissue (§ 189), and in part of non-striated muscular fibre (§ 337).
The proportion of these two components varies in arteries of different
calibre ; the muscular tissue being thicker in the smaller branches,
and the elastic tissue being found in larger amount in the main
trunks.

583. It is chiefly to the simple physical property of Elasticity, thus
possessed by the Arterial tubes, that we owe the equalization of the
flow of blood; and we may hence understand the reason, why the
trunks that are in nearest connection with the heart, should be those
most endowed with it. If a forcing- pump were to inject water, by
successive strokes, into a system of tubes with perfectly unyielding
walls, the flow of fluid at the farther extremities of these tubes would
be as much interrupted, as its entrance into them. But if the pump
be connected with an air-vessel (as in the common fire-engine), so
that a part of the force of each stroke is expended in compressing the
air, the expansion of this, during the interval between the successive
strokes, produces a continuous flow of water along the tubes. Or if
the tubes themselves were endowed wuth a certain degree of elasticity,
which should allow them to dilate near their commencement, so as to
receive the new charge of fluid, and which should occasion a con-
tinued pressure upon the fluid during the intervals of the stroke, the
same equalizing effect would be produced. This is precisely the
case with the Arterial system; the intermittent jets, by which the
blood is propelled from the heart, are speedily converted into a con-
tinued stream ; so that, at even a moderate distance from the heart,
the only indication of its interrupted action is presented by the greater
or less rapidity of the flow; and this gives rise, when an artery is
divided, to an alternate rise and fall of the jet of blood, and, in the
ordinary circulation, to the phenomenon called the pulse. This is due
to an increase in the dimensions of the arterial tube, both in length
and breadth, with each additional ingress of blood ; the increase in
length is the more considerable of the two effects, and causes the
artery to be somewhat lifted from its seat. During the intervals, a
quantity of blood corresponding to that which had entered, escapes
by the further extremity of the tube; and thus the artery is enabled
to contract to its previous dimensions, and to return to its bed. We

22

338 • EFFECTS OF MUSCULARITY OF ARTERIES.

may compare the pulse, therefore, to a wave, which commences in
the heart, and travels onwards through the arterial system.

584. In the large arteries near the heart, the pulsation is always
precisely synchronous with the ventricular systole ; but it takes place
somewhat later in the arteries at a distance from the heart; the time
•required for the transmission of the wave being proportioned to the
degree in which the walls of the arteries yield to it. If they were
quite rigid, the egress at one extremity must take place at the precise
moment that the fluid is forced into the other. On the other hand, if
the walls be too easily distensible, they yield to the propelling force
in such a degree that it is entirely expended upon them ; and the fluid
is not moved onwards at all, or but very slowly. In the healthy state
of the arterial walls, they should contract upon their contents, with
sufficient force to equalize the flow of blood, and to prevent the pulse-
wave from occupying more than one-sixth or one-seventh of a second,
in its propagation to the remotest arteries of the system ; and the pulse
should be full, producing a prolonged but gentle elevation beneath
the finger, and capable of resisting moderate pressure. This condition
is dependent in great part upon the due tonicity of the muscular coat
of the arteries (§ 365). When this tonicity is in excess, the walls of
the arteries are too rigid ; the pulse at the wrist is felt to occur exactly
at the same time with the ventricular systole; and its character is that
of strength, incompressibility, and sustained power, though it may be
even slower than usual. This is the case in what is commonly termed
*'high condition" of the system; which predisposes to inflammatory
disorders, but which renders it less susceptible than usual to the influ-
ence of malaria, contagious miasmata, or other causes of a depressing
character. On the other hand, when the tonicity of the arteries is
less than it should be, their walls yield too much to the pulse-wave ;
so that the pulse at the wrist is often felt even after the second sound
is heard ; and the pulse itself is jerking, unsteady, and too easily
compressible. This loose relaxed state of the vessels is the most
unfavourable that can be to regularity and vigour of the circulation ;
and it manifests its ill effects in the general condition of the system,
which is then peculiarly prone to suffer from the agency of malaria,
infectious miasmata, or any other depressing causes.

585. Although many Physiologists have denied that the Arteries
possess real Muscular Contractility in any degree, yet there can be no
longer any doubt on the subject; since numerous experimenters have
succeeded in producing distinct contraction in their walls, by the
application of those stimuli which act upon muscular fibre in general.
Moreover it has been ascertained, that when an artery is dilated by
the blood injected into it from the heart, it reacts with a force superior
to the impulse to which it yielded ; and that, if a portion of an artery
from an animal recently dead, in which the vital properties are still
preserved, and a similar portion from an animal that has been dead
some days, in which nothing but the elasticity remains, be distended
with equal force, the former contracts to a much greater degree than

EFFECTS OF MUSCULARITY OF ARTERIES. 339

the latter, after the distending force is withdrawn. — One use of this
contractile power may very probably be, to assist the Heart in main-
taining the flow of blood ; for if the Arterial walls yield readily to the
ingress of blood, and then contract upon their contents with a force
greater than that which distended them, the current must necessarily
be propelled onwards with greater force. This supplementary pro-
pelling force, on the part of the arteries, may serve as a compensation
to that diminution of the heart's power, which must result from the
increased friction of the blood against the walls of the vessels occa-
sioned by their subdivision ; and we thus observe, even in the highest
animals, some traces of that diffused agency, on which the Circulation
is so much more dependent in the lower tribes.

586. It seems probable, however, that one chief use of the Mus-
cularity of the Arterial walls consists in its regulation of the diameter
of the tubes, in accordance with the quantity of blood to be con-
ducted through them to any part ; the proper amount being deter-
mined by circumstances at the time. Such local changes may form
a part of ihe regular series of actions of the human body, as when
the Uterine and Mammary arteries undergo enlargement, at the
periods of pregnancy and parturition ; and they occur still more fre-
quently in diseases, which are attended by increased action of par-
ticular organs. In such cases, it cannot be vis a tergo of the Heart,
that occasions the enlargement of certain arterial trunks, and of no
others; since any increase in its propulsive power would affect all
alike. It must be, therefore, through a power inherent in themselves,
that the dilatation takes place ; and there seems much reason for
attributing to the Sympathetic system of nerves a control over this
power, and consequently the office of regulating the local distribution
of blood, in accordance with the wants of the different parts. It is
well known that the nerves of this system are copiously distributed
upon the arterial walls ; and it has been experimentally shown, that
they have the power of producing contractions in the larger arteries.
Moreover, there is every reason to believe, that the diameter of the
Capillary blood-vessels, and the rate of the movement of blood
through them, are much influenced by these nerves (§ 603); and it
seems highly probable, therefore, that they should have a correspond-
ing influence upon the size of the trunks, from w^hich these capilla-
ries are derived.

587. The Arterial system possesses nearly the same relative capa-
city in every part: that is, if a section could be made through all
the systemic arteries at a certain distance from the heart, the united
areas would be found equal to that of the aorta ; and those of the
branches of the pulmonary arteries would equal those of their trunk.
This results from the fact, that, at every subdivision, the united areas
of the branches are almost precisely equal to that of the trunk from
which they proceeded ; although the united diameters of the former
far exceed that of the latter. According to a well-known mathemati-
cal law, the areas of circles are as the squares of the diameters; con-

340 RAMIFICATION AND ANASTOMOSIS OF ARTERIES.

sequently, in making such comparisons, it is necessary to square the
diameters of the trunk and those of the branches, and to contrast the
former with the sum of the latter. Thus a trunk whose diameter is
7, may subdivide into two branches, each having a diameter of nearly
5; for the square of 7 is 49, and twice the square of 5 is 50. Or a
trunk whose diameter is 17 may subdivide into three branches, whose
diameters are 10, 10, and 9J (making 29J as the sum of the diame-
ters) ; for the square of the diameter of the trunk is 289, whilst the
sum of the squares of those of the branches, is 290:^. It appears
from Mr. Paget's recent admeasurements, that there is seldom an
exact equality between the area of the trunk and that of its branches ;
the area sometimes increasing, and sometimes diminishing. The
former seems the general rule in the upper extremities; the latter in
the lower. Thus the area of the trunk of the external carotid is to that
of its branches, as 100 to 119 ; whilst the area of the abdominal aorta,
just before its final division, is to that of its branches as 100 to 89.

588. In almost every part of their course, the ramifications of the
arteries communicate freely with each other, by anastomosis ; and this
communication is most important, as affording the means by which
the circulation is sustained, when the current through the main trunk
is obstructed. There is scarcely an artery in the body, except the
aorta, which may not be tied, with the certainty that the blood will
still be conducted to its destination, by the collateral circulation. At
first, the quantity which thus passes is very insignificant, and is by
no means sufldcient to supply what is needed ; thus, when the femoral
artery has been tied for popliteal aneurism, the limb becomes cold,
and the sensibility of its surface and its muscular powder are alike
diminished. In a few hours, however, its warmth returns, and its
sensibility and muscular power are restored ; indicating that its
circulation has been already re-established through the collateral
branches. And where an opportunity presents itself at a subsequent
period for examining the state of the vessels in such a limb, it is
found that an extraordinary enlargement has taken place in arteries
that were previously of insignificant size, which form a communica-
tion between the branches that issued above and below the inter-
ruption. Moreover, it is commonly found, that the main trunk has
become completely impervious above the part where it was oblite-
rated by the ligature, up to the point at which the nearest lateral
branch is given off. — Even the abdominal aorta has been tied in
dogs, without fatal results; the circulation in the posterior part of
the body, and in the hinder extremities, being then maintained
chiefly by the inosculation of the external mammary artery with the
epigastric, upon the parietes of the abdomen.

T>. Movement of Blood in the Capillaries.

589. The ultimate ramifications of the Arteries pass so insensibly
ifito those of the Veins, that no definite line of demarkation between

ARRANGEMENT OF CAPILLARY VESSELS, 341

them can be drawn ; and although we are in the habit of speaking of
the "Capillaries" as a distinct system of vessels, yet it ought to be
strictly borne in mind, that they differ only in size from the vessels,
from which they receive their blood on the one side, and into which
they pour it on the other. It was at one time supposed that they are
merely channels or passages, excavated in the tissues, having no
definite walls of their own. This is probably true of them in the
lower tribes of Animals ; and it may also be the case at an early
stage of their development in the higher. But when their formation
is complete, they undoubtedly possess w^alls of a fibrous texture, as
distinct as those of the arteries and veins, though of extreme thin-
ness. From the occasional appearance of bodies resembling cell-
nuclei, in the substance of the walls of the capillaries, it has been
thought that their tubes are formed, in the first instance, by the
coalescence of cells arranged in a linear direction; and this idea
receives confirmation from the fact, that the ducts of Plants are
undoubtedly formed in this manner, and not by the mere retirement
of the tissues on either side leaving an intervening channel. The
closely-reticulated structure usually formed by the capillaries, has
commonly been regarded as distinguishing them both from the arte-
ries and the veins; and it is not uncommon to speak of the arteries
as delivering the blood into the "capillary network," and the veins
as receiving the fluid that has traverseid this. Such expressions are
not incorrect as implying the simple fact, that between the arteries
and the veins is a network of minute vessels, through which the blood
has to travel when proceeding from one to the other ; but these vessels
must not be regarded as belonging to a distinct class, being nothing
else than the minutest subdivisions of the veins and arteries, which
commonly inosculate freely with each other.

590. The degree of this inosculation, and the consequent form of
the capillary network, are subject, however, to very great variations;
and these may be generally shown to
have a relation to the form of the ulti- ^'s ^^■

mate elements of the tissues, which are
traversed by the capillaries. Thus we
see in the capillaries of Muscle, that the
major part run parallel to the course of
the fibres, lying in the minute interspaces
between them (Fig. 88) ; a few^ trans-
verse branches serving to connect them

with each other. A similar distribution Capillary network of Muscle.

prevails in the capillaries of the Nervous
trunks ; but those of the Nervous centres are arranged in the form of
a minute network, so as completely to traverse every part of the struc-
ture (Fig. 89). Again, we observe that the capillaries of Glands form
a minute network around the secreting follicles (Fig. 90) ; and a simi-
lar arrangement prevails in the capillaries of the air-cells of the lungs,
which are set so closely together, that it would seem as if the purpose

342

DISTRIBUTION OF THE CAPILLARIES.

were to cover the surface with blood as completely as possible, con-
sistently with its being retained within vessels, and not spread out

Fig. 69.

Fig. 90.

Capillary Network of Nervous Centres.

Capillary Network around the follicles of
Parotid Gland.

into a continuous film (Fig. 102). A network of very much the same
character is found in the villi of the mucous membrane (Fig. 77), on
the ordinary surface of simple mucous membrane (Fig. 91), and on

Fig. 91.

Fig. 92.

Capillary Network in simple mu-
cous membrane of palpebral con-
junctiva.

Capillary Network in choroid coat
of the eye.

that of the choroid coat of the eye (Fig. 92). Where the surface of
the mucous membrane is depressed into follicles, the arrangement of
the capillaries has an evident reference to these (Fig. 93) ; whilst, on

Fig. 93.

Fig. 94.

Distribution of Capillaries around
follicles of Mucous Membrane.

Distribution of Capillaries at the sur-
face of the skin of the finger.

VARYING SIZE OF THE CAPILLARIES. 343

the other hand, where the surface of the skin is raised up into sensory
papillse, the capillary network sends looped prolongations into these,
which are found accompanying their nerves (Figs. 94 and 95.)

591. It cannot be supposed that the ar-
rangement of the vessels has any further ^'^•^^•
influence upon the function of the part they
supply, than that w^hich it derives from the
regulation of the supply of blood afforded
to each individual portion of the structure.
The form of the capillary network is evi-
dently determined by that of the elements
of the tissues permeated by it ; these are
the real operative instruments in every

part; and the distribution of the blood- papXoTthe tongue. ° ""S'*'™
vessels is so arranged, as to afford them

precisely the amount of nourishment they respectively require. Thus
we have seen, that there are many living parts, possessing most im-
portant functions, in the human body, which are not in any direct
relation with blood-vessels, and which yet derive their whole nutri-
ment, and the materials of their functional operations, from the blood.
This is the case, for example, with the whole of epithelial and epi-
dermic cells ; and also with the articular cartilages, and the substance
of the teeth. Even in bone, the islets between the Haversian canals,
which are completely unpenetrated by vessels, are of considerable
size. Such islets must everywhere exist, between the meshes of the
capillary network; so that the question of the vascularity or non-vas-
cularity of a tissue is one of degree only; — the ultimate fibre of
muscle or nerve, and the cells and fibres of other tissues, being as
completely non-vascular, as the entire substance of a tooth or of an
articular cartilage; the latter being nourished, like the former, by
imbibition from the surrounding vessels.

592. The term " Capillary" may be employed in an extended or a
restricted sense ; in the former it includes all the minute vessels,
which pass between the arteries and the veins ; in the latter it is ap-
plied only to those, which admit no more than a single file of blood-
discs at once, and excludes those, which admit two, three, or even
four rows, even although they establish a direct communication from
one side of the network to the other. The former application of the
term is the most convenient, although perhaps not the most strictly
accurate ; and it will be therefore here employed in its extended
sense. And this is rendered more correct by the fact, that the size of
the individual capillaries is by no means permanent ; an enlargeme;it
often taking place in ope, and a contraction in others, at the same
time: so that vessels, which were previously true capillaries, no
longer remain such ; and passages, which were previously of far
greater calibre, are reduced to the average diameter.

593. The opinion was long entertained, that there are vessels
adapted to the supply of the white or colourless tissues ; carrying

344 VARYING SIZE OF THE CAPILLARIES.

from the arteries only the fluid portion of the blood, or liquor sangui-
nis^ and leaving the rest behind. No other such vessels have been
really observed, however, than capillaries in a state of unusual con-
traction, as just now mentioned. And it may be safely affirmed, that
the supposition of their existence is not required. For any one who
observes the smallest capillary vessels under the microscope, may
perceiv^e, that the current of blood which passes through them is
almost free from (folour, — as the red corpuscles themselves appear to
be, when spread out in a single layer. Tissues which are rather
scantily permeated by such vessels, therefore, may still be white ; and
it is only where the network is very close, and the quantity of blood
which passes through it is consequently great, that a perceptible
colour will be communicated by the red corpuscles. And we have
seen, that the idea that Nutrition can only be carried on by direct
communication with vessels, is entirely unfounded ; the tisjsues into
which no blood-vessels can be traced, being adapted to nourish them-
selves, like cellular Plants, by the imbibition of fluid at their surfaces,
on which vessels are (for the most part) copiously distributed.

594. That the blood can only minister to the operations of Nutri-
tion, Secretion, &c., whilst it is circulating through the Capillaries,
is evident from several considerations. The thickness of the walls of
the larger vessels interposes an effectual barrier to its transudation ;
and so completely is the blood cut off, even from penetrating these,
that they do not derive their own nourishment from the blood which
flows in their own tubes, but from a capillary network in their own
substance, which is supplied by vessels from collateral branches, —
these being termed the vasa vasorum. Moreover it is by the inoscu-
lation of the capillaries alone, that the minute network is formed,
which serves to bring the blood into proximity with the minute parts
of the tissues to be nourished ; thus let it be supposed that the minute
arteries of Muscle were to terminate in veins, without undergoing
further subdivision, the islets left between their anastomosing branches
would be far too large, and the nutritive materials would consequently
not be supplied with sufficient readiness, even supposing that it could
freely permeate the walls of these vessels. — The Capillaries, then,
must not be regarded as altogether distinct in their endowments, from
the vessels with which they are connected on either side ; but merely
as intended, by their minute subdivision and inosculation, to bring
the blood into sufficiently close relation with the tissues they are to
nourish, and to allow a greater degree of transudation of its elements
by the comparative thinness of their walls.

595. When the flow of blood through the capillaries of a transpa-
rent part, such as the web of a Frog's foot, is observed with the
microscope, it appears at first to take place with great evenness and
regularity. The influence of the contractions of the heart may be
seen to extend itself into the smaller arteries ; the blood moving on-
wards in them with a somew^hat jerking motion. But this influence
altogether disappears in the Capillary network ; the flow of blood

VARIATIONS IN FLOW OF BLOOD IN CAPILLARIES. 345

through this being even and continuous, except Avhen the action of
the heart is becoming weak and irregular, or when its influence is
impeded by obstruction in the vessels leading to the part, — the blood
being then impelled by a succession of jerks, with intervals of com-
plete repose. — But on watching the movement for some time, various
changes may be observed, which cannot be attributed to the heart's
influence, and which show that a certain regulating or distributive
power exists in the walls of the capillaries, or in the tissues which
they traverse. Not only do we occasionally perceive some of the
tubes enlarging, so as to admit several files of blood-discs instead of
one, whilst others that previously received several, now only admit one ;
— but we also see vessels coming into view, which were not previously
noticed, whilst other vessels seem to become obliterated. This appa-
rently new formation and obliteration of vessels, however, do not
really take place ; for a more close examination shows, that the former
of these appearances is due to the entrance of red corpuscles into
passages, which existed before, but which w^ere in such a state of
contraction as enabled them only to admit the fluid portion of the
blood ; whilst, by a converse change in certain capillaries, from the
dilated to the contracted state, the appearance of obliteration is pro-
duced, the red corpuscles being excluded, and the transparent fluid
of the blood being alone transmitted by them.

596. But these are by no means all the irregularities, which may
be detected by a close scrutiny of the Capillary circulation. The
velocity of the current is liable to great and sudden variations, which
cannot be accounted for by any change in the heart's action, or in the
supply of blood aflforded by the arteries ; and this change may mani-
fest itself, either in the w^hole capillary network of a part, or in a por-
tion of it, — the circulation taking place with diminished rapidity in
one part, and with increased energy in another, though both are sup-
plied by the same trunk. These variations are sometimes manifested
by the complete change in the direction of the movement, in certain
of the transverse or communicating branches; this movement taking
place, of course, from the stronger towards the w^eaker current. Not
unfrequently an entire stagnation, of longer or shorter duration, pre-
cedes the reversal of the direction. Irregularities of this kind are
most frequent, when the heart's action is enfeebled or partially inter-
rupted ; and it would thus appear, that the local influences by which
they are produced, are overcome by the propelling power of the cen-
tral organ, when this is acting with its full vigour. When the whole
current has nearly stagnated, and a fresh impulse from the heart re-
news it, the movement is seldom uniform through the entire plexus
supplied by one trunk ; but is much greater in some of the tubes than
in others, — the variation being in no degree connected with their size,
and being very different in its amount at short intervals.

597. AH these circumstances indicate that the movement of blood
through the Capillaries is very much influenced by local forces ;
although these forces are not sufficiently powerful, in the higher ani-

346

MOVEMENT OF BLOOD IN CAPILLARIES.

mals, to maintain it alone. And from other facts it appears, that the
conditions necessary for the energetic flow of blood through these
vessels, are nothing else than the active performance of the nutritive
and other operations, to which they are subservient. The examina-
tion of a single one of these processes, will afford us the requisite
proof. The blood when circulating through the systemic capillaries,
yields a portion of its oxygen to the tissues it permeates, and receives
from them carbonic acid. On the other hand, when passing through
the pulmonary capillaries, it gives up its carbonic acid to the atmo-
sphere, and imbibes a fresh supply of oxygen. Now if either of
these changes be prevented from taking place, a retardation and even
a complete stagnation, of the blood will take place, — the flow through
the capillaries being now resisted, instead of accelerated, by the rela-
tion which the blood bears to the tissues. Thus it has been shown,
that if an animal be partially deprived of oxygen, so that the arterial
blood is not duly aerated (rather resembling the ordinary venous
blood), and cannot exert its proper action on the tissues, the pressure
upon the walls of the systemic arteries is increased, although the supply
of blood propelled by the heart, and the propulsive power of the
heart itself, are diminished ; and this plainly indicates a retardation in
the systemic capillaries, producing an undue accumulation in the
arteries. — On the other hand, the suspension of the supply of oxygen
to the lungs, either by an obstruction in the air-passages, or by caus-
ing the animal to breathe some other gas, brings the pulmonary cir-
culation to a stand in a very short time, the blood not being able to
undergo its usual changes in the capillaries of those organs ; and by
this stagnation, the whole movement of blood is speedily checked.
The readmission of oxygen, if the suspension of the circulation have
not been too long continued, occasions the renewal of the movement
in the capillaries, and thence in the whole circle of vessels ; and this
even after the heart has ceased to propel blood towards the lungs.

598. The principles already noticed (§ 547), as put forth by Prof.
Draper, seem fully adequate to explain these phenomena. The arte-
rial blood, — containing oxygen with which it is ready to part, and
being prepared to receive in exchange the carbonic acid which the
tissues set free, — must obviously have a greater affinity for the tissues,
than venous blood, in which both these changes have already been
effected. Consequently, upon mere physical principles, the arterial
blood, which enters the systemic capillaries on one side, must drive
before it, and expel on the other side of the network, the blood which
has become venous whilst traversing it. But if the blood which
enters the capillaries have no such affinity, no such motor power can
be developed. On the other hand, in the capillaries of the lungs,
the opposite affinities prevail. The venous blood and the air in the
pulmonary cells have a mutual attraction, which is satisfied by the
exchange of oxygen and carbonic acid that takes place through the
walls of the capillaries ; and when the blood has become arterialized,
it no longer has any attraction for the air. Upon the very same prin-

VARIOUS CONDITIONS OF CAPILLARY CIRCULATION. 347

ciple, therefore, the venous blood will drive the arterial before it, in
the pulmonary capillaries, whilst respiration is properly going on : but
if the supply of oxygen be interrupted, so that the blood is no longer
aerated, no change in the affinities takes place whilst it traverses the
capillary network ; the blood, continuing venous, still retains its need
of a change and its attraction for the walls of the capillaries ; and its
egress into the pulmonary veins is thus resisted, rather than aided, by
the force generated in the lungs.

599. The change in the condition of the blood, in regard to the
relative proportions of its oxygen and carbonic acid, is the only one
to which the Pulmonary circulation is subservient; but in the Sys-
temic circulation, the changes are of a much more complex nature, —
every distinct organ attracting to itself the peculiar substances, which
it requires as the materials of its own nutrition, and the nature of the
affinities thus generated being consequently different in each case.
But the same law holds good in all instances. Thus the blood con-
veyed to the liver by the portal vein, contains the materials at the
expense of which the bile-secreting cells are developed ; consequently
the tissue of the liver, which is principally made up of these cells,
possesses a certain degree of affinity or attraction for blood contain-
ing these materials ; and this is diminished, so soon as they have been
drawn from it into the cells around. Consequently the blood of the
portal vein will drive before it, into the hepatic vein, the blood w^hich
has traversed the capillaries of the portal system, and which has given
up, in doing so, the elements of bile to the solid tissues of the liver.
— The same principle holds good in every other case.

600. We are now prepared, therefore, to understand the general
principle, that the rapidity of the circulation of a part will depend in
great measure upon the activity of the functional changes taking place
in it, — the heart's action, and the state of the general circulation, re-
maining the same. When, by the heightened vitality, or the unusual
exercise, of a part, the changes which the blood naturally undergoes
in it are increased in amount, the affinities which draw the arterial
blood into the capillaries are stronger, and are more speedily satisfied,
and the venous blood is therefore driven out with increased energy.
Thus a larger quantity of blood will pass through the capillaries of the
part in a given time, without any enlargement of their calibre, and
even though it be somewhat diminished ; but the size of the arteries
by which it is supplied, soon undergoes an increase, which adapts it
to supply the increased demand. Any circumstance, then, which in-
creases the functional energy of a part, or stimulates it to increased
nutrition, will occasion an increase in the supply of blood, altogether
irrespectively of any change in the heart's action. This principle has
long been known, and has been expressed in the concise adage " Ubi
stimulus, ibi fluxus;" which those Physiologists, who maintain that
the Circulation is maintained and governed by the heart alone, cast
into unmerited neglect.

601. An undue acceleration of the local circulation, arising from an

348 CIRCUMSTANCES INFLUENCING CAPILLARY CIRCULATION.

excess of functional activity in the part, and unaccompanied by any
other change, constitutes the state known as active congestion, or deter-
mination of blood. This may be artificially produced by the applica-
tion of gentle stimulants; and it is usually the first change that occurs,
when their action proves sufhciently violent to produce inflammation.
From that state, how^ever, it is distinguished by this important charac-
ter,— that there is merely an exaltation of the natural function, but no
change. Moreover we shall presently see that, in Inflammation, there
is a stagnation of blood, not an acceleration. We frequently meet
with cases, in which this active congestion becomes very manifest ;
especially in persons of active minds, who exert their mental powers
too violently, and who thereby induce an habitually increased flow of
blood towards the head, manifested in the increased pulsation of the
carotids, the suflfusion of the face and eyes, and the heat of the surface.
The balance of the circulation being thus disturbed, there is almost
invariably a diminished energy of the movement of blood in other
organs, especially the extremities; as indicated by their habitual cold-
ness and lividity. In the treatment of such a state (which is often the
precursor of serious disease), it should be our object to restore the cir-
culation in the extremities, by friction, exercise, &c. ; and to abate
the flow of blood towards the head, by restraining the functional
activity of the brain, by the application of cold to the surface, by
keeping the head high during sleep, and other means of similar
tendency.

602. There is another condition of the capillary circulation, also
known under the name of Congestion, which is precisely the opposite
of the preceding. In this state, there is deficient functional energy in
the part and the circulation through it is consequently retarded, — as
in the lungs, when there is a partial obstruction to the aeration of the
blood. The same cause produces a deficient tonicity of the Arteries,
and allows their walls to be unduly distended by the vis a iergo of the
blood ; and consequently there is a great accumulation of blood in the
part with a retarded movement. This condition, like the preceding,
predisposes to Inflammation, although in a different mode, as will be
explained hereafter (§ 631). It is relieved by causes which promote
the action of the part ; thus congestion of the lungs, occasioned by the
effusion of fluid into the air-cells, which creates an obstacle to the aera-
tion of the blood disappears, when that effiision is absorbed. And
congestion of the liver, the result of deficient secreting power in the
organ, is relieved by mercurial and other medicines, which promote the
flow of bile by stimulating the growth of the hepatic cells.

603. The Capillaries, like the Arteries, possess a power of contrac-
tion and dilatation w^hich seems to be very much under the influence
of the Nervous System, and particularly of that part of it which con-
veys the influence of the Emotions. We have a visible example of
this influence, in the act of Blushing; which consists in a sudden
enlargement of the capillaries and small vessels of the surface ; whilst
the converse state of pallor^ which often alternates with it under the

MOVEMENT OF BLOOD IN CAPILLARIES AND VEINS. 349

influence of strong emotion, is evidently due to an unusual contraction
of the same vessels. But the effects of this influence are no less sen-
sible in other cases; and particularly in the regulation of the quantity
of certain secretions, in accordance with the mental state, or the con-
dition of the system generally. To the mode in which this regulation
is effected, the act of blushing seems to afford us the key ; for it indi-
cates that the supply of blood afforded to the glands, may be entirely
governed by the influence of the nervous system upon the calibre of
the arteries. Thus, the nursing mother, at the sight, or even at the
thought of her child, when the usual time for suckling approaches,
feels a rush of blood to the breast, exactly resembling that which takes
place to the cheeks in blushing, and popularly termed " the draught ;"
this rush occasions an almost immediate increase in the secretion. In
like manner we may explain the influence of the mental state upon the
amount of the secretions of the lachrymal, the salivary and many other
glands ; its influence upon their quality^ must probably be effected
through changes in the condition of the blood itself.

604. The supply of Nervous agency from the Cerebro-spinal system
has been clearly proved to exert no direct influence in maintaining the
capillary circulation; since the latter continues as usual, after all the
nerves of a part have been divided. This is obviously due to the fact,
that the operations of nutrition, secretion, &c., are essentially inde-
pendent of this agency. But as they^xe in some degree injluenced by
it, so will the capillary circulation be affected through its connection
with them. In this manner we are to explain the effect of violent
impressions upon the nervous centres in bringing to a stand, not
merely the action of the heart (§ 581), but the Capillary circulation
all over the body. The general vitality of the system appears to be
at once destroyed ; so that the capillary circulation, which may usually
be seen to continue in the web of a frog's foot for some time after the
interruption of the heart's action, is immediately suspended by crush-
ing the brain with a hammer.

6. Of the movement of Blood in the Veins,

605. The Venous system is formed by the reunion of the small
trunks which originate in the Capillary network; and it carries back
to the heart the blood which has been transmitted through this. This
blood is dark or carbonated in the systemic veins ; whilst it is bright or
oxygenated in the pulmonary veins. — The structure of the veins is
essentially the same with that of the arteries ; but the fibrous tissue of
their middle coat less decidedly exhibits the characters, either of the
yellow elastic tissue, or of non-striated muscle. Still it possesses no
inconsiderable amount of Elasticity; and a certain degree of mus-
cular Contractility also. The whole capacity of the Venous system is
at least twice^ and perhaps more nearly three times, that of the Arte-
rial ; and the rate of motion of the blood in them must be propor-
tionably slower.

330

RESPIRATORY PULSE.

606. The movement of the Blood through the Veins is, without
doubt, chiefly effected by the vis a tergo, or propulsive force, which
results from the contractile power of the heart and arteries, aided by
the power generated in the capillary vessels. The intermittent flow,
which is caused by the interrupted action of the former is usually so
far equalized during the passage of the blood through the capillary
network, that no pulsation can be shown to exist in the veins ; but in-
stances occasionally present themselves, in which a venous pulse may
be clearly perceived. — The Venous Circulation is affected, however,
by certain other causes which exert little influence on the movement of
blood in the Arteries. One of these is the frequently recurring action
of Muscles, to which the Veins are peculiarly subject, on account of
Iheir position. In every instance in which Muscular movement takes
place, a portion of the Veins of the part will undergo compression ;
;ind as the blood is prevented by the valves in the veins, from being
driven back into the small vessels, it is necessarily forced onwards
towards the heart. As each set of muscles is relaxed, the veins that
were compressed by it fill out again, to be again compressed on the
renewal of the force. Thus, we see how the general Muscular move-
ments of the body have an important influence, in maintaining the
Venous Circulation, — how continued exercise, involving the alternate
contraction and relaxation of several groups of Muscles, must send the
blood more rapidly towards the heart, and thus increase the rapidity
of its pulsations, — and how the sudden and simultaneous action of a
large number of muscles after repose (as when we rise up from the
sitting or lying to the standing posture), may drive the blood to the
heart with so violent an impetus as to produce even fatal results, if,
by any diseased condition of that organ, it should be rendered unable
to dispose with sufficient rapidity, of the quantity of blood thus driven
to it.

607. The Respiratory movements exert a slight influence upon the
flow of blood through the large veins near the heart ; for as the chest
is a closed cavity, in which a partial vacuum is produced by the act
of Inspiration, whilst its contents are compressed by the act of Expi-
ration, the former state will favour the movement of blood from the
large veins on the exterior of the cavity, towards the heart, whilst the
latter condition will retard it. This produces the phenomenon termed
the respiratory pulse; which may be seen in the veins of the neck and
shoulders in thin persons, and especially in those who are suffering
from pulmonary diseases. The influence of the Respiratory move-
ments is made evident by introducing a tube into the Jugular vein,
the lower end of which dips into water ; for an alternate elevation and
depression of the water in the tube are then witnessed, showing the
suction power of the Inspiratory movement, and the expellent force of
the Expiratory act. On the other hand, the Expiratory movement,
while it directly tends to cause accumulation in the veins, will assist
the heart in propelling the blood in the Arteries ; and by the com-
bined action of these two causes are produced, among other effects,

I

VENOUS CONGESTION.— INFLUENCE OF GRAVITY. 351

the rising and sinking of the Brain, synchronously with expiration
and inspiration, which are observed when a portion of the cranium
is removed.

608. A pulsatory movement may be occasioned in the great vems
near the heart, by another cause entirely distinct from the preceding ;
— namely, the regurgitation of blood from the ventricle into the auri-
cle, and thence into the vense cavse, during the ventricular systole ;
and the pulsation thus occasioned is synchronous, therefore, with that
in the arteries (proceeding backwards^ however, from the heart), in-
stead of corresponding with the respiratory movement. This regurg-
itation may take place, not from any disease in the valves on the right
side of the heart, but simply from over-distension of its cavities, re-
sulting from any obstruction to the circulation of blood through the
lungs, for when this occurs, the tricuspid valve does not completely
close, and allows a portion of the blood to escape from the ventricle
backwards into the auricle and vena cava. This want of complete
closure, effecting what has been termed the " safety-valve function"
of the tricuspid valve, has been particularly noticed in diving animals,
in which the circulation through the lungs is liable to be temporarily
suspended. The venous pulsation which is thus produced may be
noticed in almost every case of long-standing dyspnoea ; especially
when this is accompanied (as it usually is) by hypertrophy and dilata-
tion of the right ventricle of the heart.

609. The Venous circulation is much more liable than the Arterial,
to be influenced by the force of Gravity ; and this influence is par-
ticularly noticeable, when the tonicity of the vessels is deficient. The
following experiments performed by Dr. Williams, to elucidate the
influence of deficient firmness in the walls of the vessels, and of
gravitation, over the movement of fluids through tubes, throw great
light on the causes of Venous Congestion. A tube with two equal
arms having been fitted to a syringe, a brass tube two feet long, hav-
ing several right angles in its course, was adapted to one of them,
whilst to the other was tied a portion of a rabbit's intestine four feet
long, and of calibre double that of the brass tube, this being arranged
in curves and coils, but without angles and crossings. When the two
ends were raised to the same height, the small metal tube discharged
from two to five times the quantity of water discharged in a given time
by the larger but membranous tube; the difference being greatest, when
the strokes of the piston were most forcible and sudden, by which
the intestine was much dilated at its syringe end, but conveyed very
little more water. When the discharj^ino: ends were raised a few
inches higher, the difference increased considerably, the amount of
fluid discharged by the gut being much diminished ; and when the
ends were raised to the height of eight or ten inches, the gut ceased
to discharge, each stroke only moving the column of water in it, and
this subsiding again, without rising high enough to overflow. When
the force of the stroke was increased, the part of the intestine nearest
the syringe burst.

352 CIRCULATION WITHIN THE CRANIUM.

610. From these experiments it is easy to understand, how any
deficiency of tone in the Venous system will tend to prevent the ascent
of the blood from the depending parts of the body, and will conse-
quently occasion an increased pressure on the walls of the vessels,
and an augmentation in the quantity of blood they contain. All these
conditions are peculiarly favourable to the escape of the watery part
of the blood from the small vessels ; and this may either infiltrate into
the areolar tissue, or it may be poured into some neighbouring serous
cavity, producing dropsy. Thus it happens, that such eflfusions may
often be traced to that state of deficient vigour of the system, which
peculiarly manifests itself in want of tone of the blood-vessels ; and
that it is relieved by remedies which tend to restore this. In many
young females of leucophlegmatic temperament, for example, there
is a tendency to swelling of the feet, by cedematous effusion into the
areolar tissue, in consequence of the depending position of the limbs;
the oedema disappears during the night, but returns during the day,
and is at its maximum in the evening. And the congestion which
frequently manifests itself in the posterior parts of the body, towards
the close of exhausting diseases, in which the patient has lain much
upon his back, is attributable to a similar cause ; of such congestion,
effusions into the various serous cavities are frequent results ; and
such effusions taking place during the last hours of life, are often
erroneously regarded as the cause of death. To the same cause we
are to attribute the varicose state of the veins of the leg, which is so
common amongst persons of relaxed fibre, and especially in those
whose habits require them to be much in the erect posture ; and this
distension occasionally proceeds to complete rupture, the causes of
which are fully elucidated by the experiments just cited.

611. It has been thought that the circulation within the Cranium
takes place under different conditions from that of other parts of the
body. For as the cranium is a closed cavity, — a certain part of which
is occupied by the cerebral substance and its membranes, the remain-
der being filled up with blood, — it has been argued that the amount
of blood in the vessels of the brain must be always the same; and
that any disturbance of its circulation must be due to a difference in
the relative quantity of blood in the arteries and the veins. This
idea appeared to derive support from the results of experiments ;
which showed that the blood is retained in the vessels within the
cranium of animals bled to death, unless an opening be made in the
skull, so as to allow the air to exert the same pressure upon these
vessels, as upon those of other parts. But such experiments do not
at all sanction the assertion, that the quantity of blood within the
cranium is constant ; on the contrary, we have reason to believe that
it undergoes as much change as in other parts. For although the
cerebral substance be incompressible, yet its bulk is subject to con-
stant variation, according to the quantity of fluid it contains; and the
presence of the cerebro-spinal fluid in the sub-arachnoid cavity in the
brain and spinal cord, appears to be peculiarly destined to favour this

I

MATERIALS OF THE NUTRITIVE PROCESS. 353

continual change, — the proportions of it contained in the spinal and
cerebral cavities, respectively, being governed by the bulk of the
other contents of the cranium. Thus if the vessels of the cerebrum
be in their ordinary state of fullness, a certain amount of fluid is pre-
sent in the sub-arachnoid cavity of the brain ; this will be pressed out
into the spinal portion of the cavity, if the cerebral vessels be unusu-
ally distended with blood ; whilst it will be increased from the latter
source, so as to fill up the vacant space within the cranium, if the
cerebral vessels be unusually empty.

CHAPTER VII.

OF NUTRITION.

1. Selecting power of the Individual Parts.

612. The Blood, which is carried into the different parts of the
system, by the Circulating apparatus, is the source from which all the
organs and tissues of the body derive the materials of their growth
and development; and, as we have seen, it is distributed by the Ca-
pillaries of the several tissues, with a degree of minuteness, which
varies according to the activity of the nutrient operations taking place
in the individual parts. Thus, in Nerve and Muscle, Mucous Mem-
brane, and Skin, a constant decay of the old, and development of new
tissue, are taking place, when these organs are in a state of functional
activity ; and a copious supply of blood is carried through every part
of their substance : whilst in Cartilage and Bone, Tendon and Liga-
ment, the amount of interchange is very small, and is effected by a
much less minute reticulation of capillary blood-vessels.

613. The materials of the nutritive process being prepared in the
blood, the process of Nutrition is the act of each individual part ;
which grows and develops itself, in virtue of its own inherent
powers, as long as the requisite conditions are supplied. The mode
in which this takes place, in each individual tissue, has been already
explained in the former part of this Treatise. We have seen that, in
the great majority of cases, the act of Nutrition is, in fact, a process
of cell-growth ; and that it takes place under the same conditions, as
the production of the simple isolated cell, which constitutes the
whole of the humblest forms of Cryptogamic Vegetation, — namely,
that it grows from a germ, which draws to itself the materials of its
nutrition, and gives to some of them a new arrangement, whereby
they form the cell-wall, whilst others are introduced into the cell-
cavity, — and that, when it has passed through its regular series of
changes, it dies, and sets free its contents. We have seen that, in

23

354 SYMMETRY OF THE NUTRITIVE PROCESSES.

some cases, the germs are prepared by previously existing cells of
the same kind ; whilst in others they are furnished by certain " nutri-
tive centres," which seem to be constantly engaged in the preparation
of them, deriving their materials from the blood. Frequently it would
seem as if the original or parent-cell was able to continue the pro-
duction of secondary cells to an unlimited extent, even though it has
itself undergone a considerable change of form. Thus the ultimate
follicles of Glands seem to be at first closed cells, which subsequently
open at the part nearest to the .duct, and establish a connection
with it ; and having thus changed their condition, they go on deve-
loping new generations of secreting-cells in their interior, from their
own nuclei or germinal centres, to an unlimited extent. In like
manner, the parent-cells of Muscular Fibre, which have coalesced to
form the tubular Myolemma, seem to continue to develop new fibrillse
from their nuclei, notwithstanding their change of form.

614. The selecting power, which is possessed by the germs of each
kind of tissue, and which enables them to draw from the blood the
materials which they severally require for their development, mani-
fests itself also in the mode in which substances, that are abnormally
present in the blood, affect the condition and development of the
solid tissues. Thus we find that the presence of a certain quantity
of Arsenic in the blood, will produce a state of irritation in all the
Mucous membranes of the body. The continued introduction of Lead
into the circulating system, occasions a modification in the nutrition
of the extensor muscles of the fore-arm, producing the form of partial
paralysis commonly termed wrist-drop; and the existence of this
modification is shown, by the presence of lead in the palsied muscles.
Here we have to remark the symmetrical nature of the affection, con-
sequent upon the occurrence of the same disorder in the corresponding
parts of the two sides of the body; for these muscles appear to have
the same kind of tendency to attract lead from the circulating current,
in a degree that is equal on the two sides, as they have to draw from
the blood the materials of their regular growth, and to develop them-
selves in an exactly similar manner. In like manner, the cutaneous
eruptions, which are occasionally produced by the internal exhibition
of iodide of potassium, are found to be almost precisely symmetrical;
the presence of the medicine in the blood being the occasion of a
disordered nutrition of certain parts of the skin ; and the selecting
power of particular spots being evinced, by the exact correspondence
of the parts affected on the two sides.

615. The same appears to be the case with regard to substances,
w^hose presence in the blood is rather the result of a disordered con-
dition of the digestive and assimilating processes, than of their direct
introduction from without. Thus in Lepra and Psoriasis, — chronic
diseases of the Skin, which seem to have their origin in a disordered
state of the blood, rather than in the solid tissues affected, — we find a
remarkable tendency to the repetition of the patches, on the two sides
of the body, or on the corresponding parts of the limbs ; and this we

>

I

UNUSUAL ENERGY OF THE NUTRITIVE PROCESSES. 355

must attribute to the peculiar attraction, existing between the solid
tissues of those parts, and the morbid matter circulating through them.
So in those chronic forms of Gout and Rheumatism, which modify
the nutrition of the joints, producing a deposit of *^ chalk-stones," or
permanent distortion and stiffening, we almost invariably find the
corresponding joints of the two sides affected. The chief exceptions
to the general principle, that the presence of morbid or extraneous
matters in the blood affects corresponding parts alike, are found to
exist where there is much febrile disturbance, or where local causes
produce a peculiar tendency to disorder of a single part. The nearer
the character of the morbid process is to that of the ordinary nutritive
operations, the more nearly does it approach these, in the symmetry
with which it develops itself.*

2. Varying Activity of the JVutritive Processes.

616. The nutritive operations go on with very great variations in
their relative activity, under different circumstances. As a general
rule it may be stated that, the greater the demand for the functional
activity of the organ or tissue, the more energetic is its nutrition ; and
vice versa. Now this is readily understood, when it is considered,
that the active state of many structures essentially consists in an act
of nutrition ; thus the energy of the secreting processes is really de-
pendent, as we have seen, upon the growth of the secreting cells,
which make up the essential part of the gland ; and the energy of the
absorbing and assimilating processes is dependent upon the develop-
ment of the cells, which select and elaborate the nutrient matter.
This growth is regulated mainly by the supply of blood ; being
increased by the afflux of blood towards the part, in consequence of
the influence of the nerves upon the vessels, or through any other
change in the current of the circulation. Thus the secretions are
increased in amount, by emotions of the mind, that act (probably
through the sympathetic nerve), in regulating the calibre of the arteries
supplying their respective glands; or the interruption of the function
of one gland shall occasion an increased nutrition, and consequently
an augmented secretion, in its fellow, — as when one of the kidneys
is hypertrophied, through a disease in the other, that renders it inca-
pable of performing its office. Still it would appear, that there may
be variations in the activity of these organs, resulting fram causes
inherent in themselves (of the nature of which we know little or
nothing); and that here, as elsewhere, active nutritive operations will
promote the circulation of blood through the parts, whilst a languid
state of the function will retard it.

617. In certain other tissues, however, the functional activity would
seem to be dependent rather upon a waste or decay of structures pre-
viously developed ; this is the case especially in Nerve and Muscle,

• See Dr. W. Budd's valuable paper on the "Symmetry of Disease," in vol. xxv. of
the Medico-Chirurgical Transactions.

356 VARIOUS CAUSES OF HYPERTROPHY.

which are found to undergo disintegration, in exact proportion to the
degree in which they are exercised; whilst the degree in which this
waste is repaired, depends upon the supply of nutritive material, the
quiescent state of the part, and other circumstances. But even here
we find, that functional activity occasions increased nutrition ; in the
same manner as burning a lamp with a high flame increases the
amount of fluid drawn up by the wick. For neither the nerves nor
the muscles can act with energy, without a large supply of arterial
blood ; and this is drawn to them on the principles already mentioned,
as increasing the energy of the local circulation (§ 600). The deter-
mination of blood to the parts, thus established, favours their increased
nutrition ; and thus we find that, under favourable circumstances,
any set of Muscles, which is habitually exercised, undergoes a great
increase of development; whilst, in like manner the Nervous centres,
if too great a demand be made upon their activity, are liable to
become hypertrophied (especially in young persons), and may thus
become subject to disorders, which temporarily or permanently de-
stroy their powers. In these cases, then, the functional activity
determines the increased supply of blood, and occasions the aug-
inented growth ; and increased nutrition will rarely take place in
these tissues, without an especial stimulus of this kind. Thus we find
that, when a larger supply of nutritive matter is introduced into the
circulation, than is required to repair the waste of these tissues, they
do not undergo an increased development in consequence ; but an
augmented nutrition is produced, either in the adipose tissue, or in
the glandular structures by which the superfluous matter is eliminated
from the system.

618. Augmented nutrition, or Hypertrophy^ then, may result, in
certain organs, from an excessive supply of their nutrient materials ;
as in the case of the kidney just mentioned ; or as in the enlargement
which we not unfrequently meet with in the livers of those who have
resided long in warm climates, and who have not suflSciently restricted
their supply of non-azotized food to the small amount required for
respiration at an elevated temperature, thereby sending an over-sup-
ply of that particular class of bodies, to be separated from the blood
by the liver. Or, in other cases, the increase of functional activity
may be the immediate cause of the increased nutrition ; and this we
see, not only in the nervous centres and voluntary muscles, which
are put in action by the will, but in parts over which the mind has
no control. Thus the heart becomes hypertrophied, when an obstruc-
tion exists in the pulmonary or systemic circulation, to overcome
which, increased energy of contraction is required ; and in the same
manner, the muscular coats of the urinary and gall-bladders acquire
an extraordinary increase of thickness, when long-continued obstruc-
tion, by calculi or stricture in the canals issuing from them, impedes
the free exit of their contents. Sometimes, however, a local hyper-
trophy takes place, which cannot be accounted for in either of these
modes ; as when a single finger is enlarged out of all proportion to

VARIOUS CAUSES OF ATROPHY. 357

the rest, or the whole of one hand increases to a much greater size
than the other, by the existence (as it would seem) in the individual
part, of that tendency to unusual development, which, when it affects
the whole body uniformly, produces a gigantic stature.

619. Now a precisely reversed series of conditions diminishes the
activity of the nutrient processes, and induces a state of Atrophy. If
there be a deficiency in the general amount of nutriment introduced
into the system by absorption, 2, general atrophy results; and the waste
being more rapid than the supply, there is a diminution in the volume
of all the tissues excepting the nervous, which seems to have its nu-
trition kept up even to the last, at the expense of all the rest. Such
a condition results not merely from the want of food, but also from
the want of power to assimilate it ; and thus emaciation may take place
to an excessive degree, when food of the most nutritive character is
copiously applied, and when the appetite for it is vehement; in con-
sequence of disorder in the mesenteric glands, or in some other part
of the apparatus particularly concerned in the elaboration of fibrin. A
partial atrophy may result, in like manner, from a deficiency of the
materials required for the formation of an individual tissue or organ ;
thus the adipose tissue, throughout the body, may be atrophied, in
consequence of an absence of those materials in the food, which are
capable of being converted into fatty matter. Or a particular organ
may be atrophied, by a diminution of the circulating current that
should flow to it, either in consequence of obstruction in the trunk,
or by the partial diversion of the stream of blood in another direc-
tion ; thus the liver, which is much more developed in the fcetus,
relatively to the rest of the body, than it is in the adult, undergoes a
partial atrophy immediately after birth, in consequence of the change
in the whole course of the circulation, which takes place as soon as
the lungs are expanded.

620. But partial atrophy may also take place from causes inherent
in a particular organ. Thus we occasionally meet with limbs, which
are '^ blighted ;" never attaining their due size relatively to the re-
mainder of the body; yet not exhibiting any defect of organization.
Here there would seem to be, from some unknown cause, a deficient
power of growth; analogous to that which, w^hen acting on the body
in general, confines it within dwarfish dimensions. — One of the most
frequent causes of partial atrophy, however, is want of functional ac-
tivity in the organ ; and this is particularly the case in regard to the
Muscular and Nervous systems. Thus, as already remarked (§ 348),
any set of Muscles that is long disused, becomes partially atrophied ;
which is probably due to the feebleness and languor of the circula-
tion, consequent upon the absence of the demand for arterial blood.
As soon as the parts are called into use again, their nutrition improves.
So, also, in regard to the Nerves ; the nutrition of both the fibrous
and vesicular structures appears to be entirely dependent upon the
activity of their function ; and as the former are inert without the lat-
ter, we may say that the due nutrition of the nervous system entirely

358 VARYING ACTIVITY OF THE NUTRITIVE PROCESSES.

depends upon the functional activity of the vesicular matter. Of this
we have a well-marked illustration in the fact, that, when the Cornea
has been rendered so opaque by disease or accident, as to prevent
the penetration of any light to the interior of the eye, the retina and
the optic nerve lose after a time their characteristic structure; so that
scarcely a trace of the peculiar globules of the former, or of the nerve-
tubes of the latter, can be found in them.

621. In the healthy condition of the organism, however, the nutri-
tion of every part of the body goes on in a degree sufficient to keep
it constantly ready for the performance of its appropriate function ; a
regular supply of the requisite materials being furnished in the aliment,
and being prepared by the assimilating processes ; and the products
of the waste or decay of the tissues, together with such alimentary
materials as maybe superfluous, being carried off by the excreting
operations. When the nutrition and the waste are equal, the weight
of the body remains the same ; and this is commonly the case in
adult age. But during the earlier periods of life, the powers of
growth are greater ; the demand for food is very large, in proportion
to the bulk of the body ; and though the waste is rapid and the ex-
creting processes very active (as evinced by the large amount of urea
and of carbonic acid set free), the growth predominates over the
decay, and the development of the whole structure proceeds at a gra-
dually decreasing rate, until the full stature and bulk are attained.
The energy of the nutritive process is particularly manifested in the
rapidity and completeness with which severe injuries, occasioned by
disease or accident, are repaired. In advanced life, on the contrary,
although the waste is comparatively small, the renewing processes are
enfeebled in a still greater degree ; and there is a gradual diminution
in the stature and bulk of the body, and in its physical powers. All
the functions are performed with diminished energy ; and the compa-
rative inertness of the nutritive processes is seen in the difficulty
with which the effects of severe injuries are repaired, in the length of
time requisite for the purpose, and frequently in the imperfection of
the result.

622. During the successive periods of life, there are many remark-
able changes in the relative nutrition of different organs ; which we
can attribute to nothing else than to inherent differences in their own
powers of development. Thus, during the early stages of fcetal exist-
ence, the greatest energy of growth is seen in certain parts, which are
to answer but a temporary purpose, and which are afterwards com-
pletely atrophied. This is the case, for example, with the Corpora
Wolffiana, which seem to answer the purpose of temporary kidneys,
and in connection with which the permanent kidneys and the genital
organs are developed ; and of these bodies, though of large size in the
early embryo, and evidently of great importance, no trace whatever is
afterwards to be discovered. So in regard to the Supra-Renal cap-
sules, the Thymus and Thyroid glands, and other organs, we find their
proportional size the greatest, and their function evidently the most

VARIATIONS OF NUTRITION WITH AGE. 359

active, during fetal existence and in early infancy ; after which their
bulk diminishes in proportion to the rest of the body, and their func-
tional activity seems ahnost at an end.

623. Even in the relative development of the organs, which form
essential parts of the permanent structure, we find considerable varia-
tions at different periods of life. Thus the evolution of the generative
system does not usually take place, until the rest of the system is ap-
proaching its maturity ; but cases sometimes occur, in which this appa-
ratus attains its full development, both in the male and the female,
at a very early period of childhood, and seems capable of performing
its functions. In the Human species, these organs, when once evolved,
remain always in a state of preparation for the performance of their
function, unless they are atrophied through complete disuse, or have
lost their vigour by age, or through excessive demands upon their
activity ; but in most of the lower animals, the development of these
organs is periodical through the whole of life, taking place at a cer-
tain season of the year, and being greatly influenced, it would ap-
pear, by the external temperature, and by the supply of food. Thus
in the Sparrow, the testes are no larger than mustard-seeds, during
the greatest part of the year; but in the spring, they acquire the size
of large peas, and it is then only that they possess any procreative
power.

624. We are not always to judge of the degree of development of
organs, however, by their size alone ; for the completeness of their
structure, and their aptitude for the performance of their functions,
must also be taken into the account. Thus in the new-born infant,
the organs of digestion and assimilation, though of small size, are so
completely formed, as to be able at once to take on the duty of re-
ceiving and preparing the nutritive materials, provided these are sup-
plied in a form adapted to their powers; the circulating apparatus is
fully adequate to transmit the products of the action of those organs to
the body in general, and to bring back the results of its continual
decay ; and the respiratory organs, together with other parts of the
excretory apparatus, are so completely evolved, as to be able to sepa-
rate the effete matter, and cast it out of the system, with an energy
equivalent to that of the organs, by which new matter is introduced
and appropriated. On the other hand, the Brain, although of larger
comparative size at birth, than at any subsequent period of life, is but
very imperfectly developed ; for its structure is not yet so far com-
pleted, as to prepare it for a state of high functional activity. In fact,
it would seem as if the use of the organ, as called forth by the new
circumstances in which the infant is placed as soon as it comes into
the world, is essential to its complete development ; and the same may
be said of the Muscular system.

625. During the whole period of infancy and childhood, the current
of nutrition seems peculiarly directed towards the brain ; for though
its size does not continue to increase in proportion with that of the
remainder of the body, its structure is evidently being rendered more

360 VARIATIONS OF NUTRITION WITH AGE.

perfect, and its functional activity is excited with remarkable facility.
Hence it is peculiarly liable to be acted on by various causes, which
may produce disease ; and the operation of remedies, which spe- '
cially affect that organ, is far more powerful than at any other period
of life. Thus, whilst a child will bear a fourth, or even a third, of the
dose of a purgative adequate for an adult, it is strongly affected by an
eighth, or even a twelfth, of the dose of a narcotic or a stimulant, that
would be required to produce a corresponding effect in middle life.
This peculiar impressibility of the nervous system, resulting from the
activity of the nutrient processes which are taking place in it, mani-
fests itself also in other ways ; thus children are peculiarly liable to
have its powers depressed by any sudden shock, such as a blow, or an
extensive burn or laceration; whilst, on the other hand, if the depres-
sion be not fatal, they recover from its effects much more speedily than
an adult would do from a similar condition.

626. During the periods of youth and adolescence, the chief energy
of development (except in regard to the generative system, already
noticed), appears to be directed towards the Muscular apparatus;
which then increases in vigour, in a degree which surpasses its
increase of size ; and the circulating and respiratory organs, upon
whose energetic action there is then a corresponding demand, are
peculiarly liable to disturbance of function, inducing disease in them-
selves or in other parts. The maladies of this period are for the most
part of a sthenic or inflammatory character ; resulting, as we shall
presently see, from the excessive activity of the assimilating pro-
cesses, which are disposed to produce more fibrin than the wants of
the body require. Or if, on the other hand, there be an imperfect
elaboration of the nutrient materials, as happens in the tubercular
diathesis, its effects are peculiarly liable to manifest themselves at
this period, when the demand for nutritive matter is greatly aug-
mented by the activity of the muscular system.

627. In adult age, there should be such a balance of all the func-
tions, arising from the due development and proper use of each organ,
as may preserve the body in the state of health and vigour, without
any marked change in the relative dimensions of its different parts,
through a long series of years. The digestive, assimilating, and
excreting organs, as they were the first to come to maturity, are com-
monly the first to fail in their activity; but this is very generally the
result of over-exertion of their powers, the amount of food introduced
into the stomach being rarely (among the higher and middle classes
of society at least) kept down to the real wants of the system. The
muscular apparatus usually experiences the effects of this diminished
nutrition sooner than the nervous system ; the vigour of the latter
being often sustained in a remarkable degree (as shown by the energy
of the mental operations) through a protracted life, when it has not
been over-tasked at an earlier period. The very slight impairment
of the nutrition of the nervous system, during the general emaciation
which results from a wasting disease, or during that more gradual

VARIOUS CAUSES OF DEATH. 361

decline of the bodily vigour which is consequent upon advancing
age, is a phenomenon which strongly marks it out as the part of the
body, to the maintenance of whose integrity everything else is sub-
servient; and this is still more remarkably shown in the phenomena
of starvation ; in which, notwithstanding the disappearance of the
whole of the fat, and the reduction of the weight of the body in general
by about 40 per cent., the nervous system appears to lose little or none
of its substance (§ 117).

3. Of Death , or Cessation of JVutrition.

628. The general cessation of the Nutritive operations^ in Death,
usually depends, as formerly explained (§ 65), upon the cessation of
the supply of Nutriment, in consequence of the stagnation of the Cir-
culating current ; and this stagnation may result from the direct ope-
ration of three causes ; namely, — failure in the propulsive power of
the Heart, or Syncope, — obstruction to the flow of blood through the
pulmonary capillaries, consequent upon a deficient supply of air, or
Asphyxia, — and a disordered state of the blood itself (§ 534), which
at the same time weakens the power of the heart, and prevents the
performance of those changes in the systemic capillaries, which afford
a powerful auxiliary to the circulation ; a mode of death, for which
the term JVecrcemia has been proposed. Each of these conditions may
be dependent upon a variety of remote causes, which need not here
be particularized. But it is evident that, when either one of them
has been established, the nutritive processes must speedily cease,
although they may continue for a short time at the expense of the
blood in the capillaries of the part. The cooling of the body is
another cause of their cessation ; and this is one reason why molecular
death (or the death of the individual organs and tissues) follows so
much more closely on somatic death (or the cessation of the circula-
ting and respiratory functions), in warm-blooded than in cold-blooded
animals. In either case, however, the solid tissues may preserve for
a time their independent vitality ; and changes may take place in
them, which indicate the continuance of their nutritive actions to a
certain extent, even when they have been disconnected from the body.

629. Although the death of the several parts composing the fabric
is thus due, in the great majority of cases, to the supensions of the
supply of the nutritive materials, and to the lowering of the tempera-
ture of the body, yet there are undoubtedly cases, in which the loss
of vital power is as complete in the solids as in the fluids ; the want
of ability to avail themselves of nutriment, being as decided in the
former, as the deficiency of supply is in the latter. This is seen, for
example, when death results from a sudden and violent shock, which
destroys the vitality of the whole system alike (§ 604). But it can
scarcely be doubted, that we are to attribute the gradual decay and
death, which take place in extreme old age without any symptom of
local disease, to a similar cause. We have seen that every individual

362 NATURAL DEATH.— INFLAMMATION.

part of the fabric has its own allotted period of life and activity ; each
cell passing through a certain series of changes, which are proper to
it, and then ceasing to exist ; and many organs having only a limited
period of activity, and disappearing more or less completely, when
this has been accomplished. In both cases, the usual duration of the
organ is usually diminished by any previous excess of activity, and
increased by moderation in the exercise of its vigour. Thus, the life
of the individual cells of the simple cellular plants (on which our
observations as to some of the conditions of cell-growth may be best
made), is shortened by such external influences as are most favourable
to rapidity in their growth and development. And in Man, we con-
stantly notice that the duration of the powers of the Brain and the
Generative system is the longest, when these organs have been mode-
rately exercised ; and that it is much curtailed by the excessive use of
either. The duration of their activity, however, is not increased by
partial or entire disuse of the organs ; for this induces a state of
atrophy, on the principles already mentioned. Now we have every
reason to believe, that what is true of individual parts and organs, is
true also of the whole structure ; and that the existence of the entire
bodily fabric may thus come to an end, without any special disease,
in consequence of the limit originally set to its powers of self-renova-
tion. It is but rarely, however, that this occurs ; the various acci-
dents of life, the neglect of ordinary precautions for the preservation
of health, and hereditary tendencies to various kinds of morbid action,
being too frequently the means of cutting off' the term of Human
existence, long before its natural expiration.

4. Disordered Conditions of the JVutritive Processes.

630. Having thus passed in review the general conditions, under
which the ordinary Nutritive processes take place, it may be well to
add a few w^ords in relation to two of their abnormal states ; one or
other of which is concerned in a very large proportion of the diseases
that afflict the human race. In one of these, there is a tendency to
the excessive production of Fibrin in the blood ; whilst in the other,
there is a want of the proper nutritive power in the tissues, which is
apparently due to an imperfect elaboration of that important material.
The one of these conditions is termed Inflammation; whilst the other,
which is less active, but more insidious, is known as the Tubercular
Diathesis.

631. The extraordinary tendency to the production of Fibrin in
the blood, which has been already noticed (§ 531) as the most import-
ant character of Inflammation, seems to be always conjoined with a
depressed vitality of the tissues of some part of the body, which indis-
poses them to the performance of their regular nutritive operations ;
and this part may undergo a variety of changes, according to the
degree in which it is affected. The depressed condition of its nutri-
tive operations involves, on the principles explained in the preceding

INFLAMMATION 5 SUPPURATION; GANGRENE. 363

chapter, a languor in the movement of blood through it, together with
a distensible state of the capillaries, which causes them to contain a
far greater amount of that fluid than under ordinary circumstances.
There appears to be, in the vessels of an inflamed part, a peculiar
attraction for the white corpuscles of the blood, by which they are
drawn together from the circulating current ; and there is also a tend-
ency to an increased production of them, which is probably the cause
of the increase in the total amount of fibrin. This increase of fibrin
in the blood, coupled with a diminished power of appropriating it on
the part of the tissues, appears to constitute the essential phenomena
of the Inflammatory condition, and to be the cause of the other changes
which are characteristic of it.

632. The simplest result of this condition, is the effusion of fibri-
nous matter, or organizable lymph, into the substance of the part
inflamed, or upon the nearest free surface; and thus is produced a
condensation of the tissue, or a new growth upon the membrane.
But when the depression of vitality is more complete, the tissue at
that spot gradually dies and disintegrates ; and whilst itself undergo-
ing such changes, it gives origin to similar changes in the eff*used
fibrin, which it converts from ?i plastic or organizable deposit, into an
aplastic or unorganizable one, namely, pus. Thus is produced the
Suppurating process ; which may either take place in a cavity thus
excavated in the substance of a tissue or organ ; or on a free surface.
In either case, the surrounding tissues, which are less inflamed, and
in which the vitality is impaired but not destroyed, become consoli-
dated by a deposition of organizable fibrin, which prevents the infil-
tration of pus through their substance. If this should not occur,
through a want of power to generate well-elaborated fibrin, the sup-
purating process extends itself rapidly, with the most calamitous
results; the properties of pus being such as to produce a tendency
to decomposition, both in the blood and in the solid tissues into the
substance of which it may be carried.

633. The process termed Gangrene^ which is the entire loss of vi-
tality in the part, with a complete cessation of the circulation through
it, is commonly ranked as one of the results of Inflammation ; but it
can hardly, in strictness, be so regarded. We have a well-marked
illustration of the mode in which this local death takes place, in the
case of frost-bites produced by Cold ; for this agent at the same time
produces contraction of the blood-vessels, and depression of the vital
powers of the solid tissues, proceeding to the complete destruction of
them; whilst in the parts adjoining those which are actually killed,
the inflammatory state is developed ; producing an effusion of fibrin,
which serves to plug up the mouths of the vessels, and thus to prevent
hemorrhage, when the mortified part drops off*. Here we see, that
the violent action of cold completely destroys the vitality of the part
most exposed to it; and this by its direct influence on the properties
of the organized structure. No inflammation can take place in the
part thus killed, because the vital processes are altogether brought to

364 GANGRENE; ULCERATION.— REPARATIVE PROCESS.

an end. But inflammation takes place in the adjoining parts, which
are less seriously affected ; for the depression of their vital powers
occasions the result already adverted to, — namely, the production of
an increased amount of Fibrin in the blood, and an infiltration of
this substance into their tissues. The same is the case with regard
to the operation of other powerful agents ; such as those which (like
Caustic potass, or Sulphuric Acid) destroy the vitality of the parts to
which they are applied, by the chemical decomposition of their tis-
sues. The Inflammatory process is set up, not in the parts which are
killed by the application ; but in the surrounding tissues, whose
vitality has been simply depressed ; and thus, when the slough, or
dead part, is cast off*, there is a preparation for the development of
new tissue to supply its place, from the superabundant plastic mate-
rials of the surrounding parts.

634. If, then, we limit the term Inflammation, as there seems
reason to do, to that state, in which there is a tendency to stagnated
circulation, with increased production of Fibrin, in the vessels of the
part, we see that Gangrene cannot be a result of that process, which
is one rather of reparation than of destruction. But Gangrene pro-
ceeds, where we can distinctly trace its causes, from the violent ope-
ration of the same agents, as those which, in a less degree, produce
Inflammation. And where this last process is not set up, at the line
of demarkation between the living and the dead parts, Gangrene, like
Suppuration, has a tendency to spread ; the influence of the decay,
which is taking place in one part, having a tendency to propagate
itself to the adjoining tissues ; and a constantly extending destruction
being thus produced.

635. In like manner, certain forms of the Ulcerating process may
spread, by the action of a peculiat layer of cells, that is found on the
surface of the excavation ; these cells appear to possess the power of
drawing into themselves the materials of the solid tissues on which
they lie, and thus of causing their destruction; and this destructive
action may take place to an unlimited degree, if no measures betaken
to check it. The application of powerful escharotics (such as nitric
acid, lunar caustic, or the actual cautery), which is w^ell known to be
one of the most efficient methods of treatment in this kind of diseased
action, has the effect of destroying these peculiar cells, together with
the adjacent tissue which has been partly affected by them; and of
exciting an inflammatory action beneath, by which fibrin may be
effused, and preparation made for filling up the breach of substance.

636. Now when the reparation of lost parts takes place, it may be
effected in either of two modes ; — by a process of growth analogous
to the natural one ; — or by the formation of a new kind of tissue,
termed granulation-structure, from the surface of which a formation
of pus takes place, until the cavity is completely filled up by it, and
closed over by skin, after which the granulation-structure is absorbed,
and a contracted cicatrice is left. The former mode of reparation,
which takes place in cold-blooded animals, is the slowest, but it is

REPARATIVE PROCESSES.—TUBERCULAR DIATHESIS. 365

the most complete ; for as the breach of substance is filled up by
tissue of a permanent kind, there is no subsequent contraction nor
cicatrix ; nor is there that waste of plastic matter, nor that constitu-
tional irritation, which is attendant on the suppurating process. It
is, consequently, that which the Surgeon should aim to produce ; and
the means of accomplishing this consists in keeping down the Inflam-
matory process, and in preventing irritation of the exposed surface.

637. In all cases of injury, there is an increased determination of
blood to the neighbouring tissues; and an increased production of
Fibrin, to serve as the material for repair. Now if this be moderate
in its amount (as it usually is in cold-blooded animals), it will be all
consumed in the formation of the new tissue, which is to fill up the
vacuity. But if it be excessive, it forms an inflammatory eflTusion ;
part of which undergoes a low degree of organization, and becomes
granulation-structure ; whilst another part is poured forth from the
copious but imperfectly-formed vessels of that structure, in an unor-
ganizable state, forming Pus. This change in its character is mainly
due to the irritating influence of cold air; which also tends to keep
up the excessive production of Fibrin by the Inflammatory process;
and the more carefully the raw surface is kept from contact with it,
the more healthy will be its action. The low temperature of cold-
blooded animals prevents the air from having a like injurious eflfect
upon their wounded surfaces ; no exclusion of it seems necessary. In
warm-blooded animals the desired end may be attained, either by the
application of hot dry air, which causes a scab to form, beneath which
the reparative process may take place in complete seclusion from
external irritation ; or by the formation of an artificial covering,
equally closely applied, by means of a waxy or resinous ointment,
spread in a liquid state (a measure which has proved peculiarly effi-
cacious in the treatment of burns) ; or by the application of steam to
the wounded surface, w^hich seems to have a remarkably soothing
effect upon it ; or, where there is a tendency to violent inflammation
(as in wounds of the large joints), by keeping the dressings moist by
a continual supply of cool (but not cold) water. All these modes of
treatment act in the same manner ; tending to exclude irritation, to
keep down inflammation, to prevent the over-production of fibrin,
and to promote the natural process of slow reparative growth.

638. If the Fibrin of the Blood, however, be not well elaborated,
it does not possess its due organizability ; and thus, instead of being
converted by the Nutritive process into solid tissue, proper to the part
in which it is deposited, it is liberated from the vessels in a state,
which prevents any but a very imperfect structure from being deve-
loped by it. This is the condition of the Tubercular substance, which
is so often found to replace the proper tissue, especially in the lungs ;
being slowly deposited there, by a sort of degradation of the regular
nutritive operations ; and being effused in larger quantity, when the
inflammatory process is set up. There is every degree of gradation
between the plastic or organizable deposit of well-elaborated Fibrin,

366 TUBERCULAR DIATHESIS.— MALIGNANT GROWTHS.

the caco'plastic or imperfecily-organizahle matter of Tubercle, and the
aplastic or non-organizable matter of Pus. The Microscopic exami-
nation of tubercular deposit shows, that they sometimes contain fully
developed cells and fibres, analogous to those of fibrinous exudations ;
but that more frequently, the cells and fibres are imperfectly formed,
and are accompanied by a- large quantity of a granular substance,
which strongly resembles coagulated Albumen ; and that in many
cases, there is scarcely any trace of organization in the mass. The
greatest degree of organization is found in the semi-transparent, mili-
ary, gray, and tough yellow forms of Tubercle ; the least in the opaque,
crude, or yellow Tubercle.

639. The constitutional state, w-hich predisposes to this perversion
of the ordinary nutritive operations, and which is known as the Tu-
bercular Diathesis, is the result of the continued operation of any
causes, that tend to depress the vital powers ; such as insuflScient
nutrition, habitual exposure to cold and damp, protracted mental
depression, &c. ; or it may be derived from the operation of the same
or other causes on the ancestors of the individual, being one of those
disorders which has a peculiar tendency to become hereditary. The
treatment must be directed to the invigoration of the system by good
food, active exercise, pure air, warm clothing, and cheerful occupa-
tions ; and by the due employment of those means, at a sufficiently
early period, many valuable lives may be saved, which would other-
wise fall a sacrifice to Tubercular disease in the lungs, or other import-
ant organs.

640. There is another remarkable class of diseases, resulting from
a disordered condition of the nutritive processes ; — those, namely, of
a malignant nature. We not unfrequently meet with abnormal growths
of a fatty, cartilaginous, fibrous, or bony structure ; which appear to
originate in some perverted action of the part itself, and which have
little tendency to reappear in the same part, w^hen they have been
removed, — still less, to reappear in distant parts. But the various
forms of Malignant or Cancerous disease are peculiar in this, — that
they are composed of cells, sometimes of a globular form, (see Fig.
30), sometimes elongated or spindle-shaped, having a power of rapid
multiplication, and not capable of changing into any other kind of
tissue. When a truly cancerous growth has once established itself in
any part of the body, it may increase to an unlimited extent, obtain-
ing its nourishment from the blood-vessels in its neighbourhood, and
destroying the surrounding parts by its pressure, as well as by draw-
ing off their supply of aliment. When it has developed itself to a
considerable degree in one part, it is very liable to make its appear-
ance in others; probably in consequence of the germs of the cells
being conveyed in the circulating current to distant portions of the
body: and hence the judicious surgeon is disinclined to remove a
Cancerous growth of any but the most limited kind; knowing that
the disease is almost certain to reappear. There is a strong analogy
betw^een such Cancerous growths, and the low forms of Fungoid

NEED OF RESPIRATION IN ANIMALS. 367

Vegetation, which develop themselves in the interior of the higher
Plants, and even in Animal bodies ; and in both cases, the disease
may be propagated by inoculation from one individual to another, the
transplantation of a few cell-germs being all that is required.

CHAPTER VIII.

OF RESPIRATION.

1 . Essential Mature and Conditions of the Respiratory Process.

641. The function of Respiration essentially consists of an inter-
change of oxygen and carbonic acid between the blood of the Animal
and the surrounding medium ; carbonic acid being given out by the
blood, and oxygen entering in its stead. . It has been already noticed
(§ 84) that this function is performed likewise by Plants; although,
in consequence of their deriving a large part of their food from the
atmosphere by a converse process — the absorption of carbon and the
liberation of oxygen, — their true respiration is commonly overlooked.
It may, therefore, be regarded as common to all Organized beings.
Every one is conscious, in his own person, of the imperative demand
for the due performance of this operation. If the breath be purposely
held for even a few seconds, a feeling of distress is experienced,
which increases every moment, and at last prompts irresistibly to the
respiratory movement. And if the admission of air to the lungs be in
any way prevented, the respiratory movements are at first increased
in energy, violent efforts are made to obtain the needed supply; these
are succeeded by irregular convulsive actions, and at the same time
insensibility comes on ; and within a short time all movement ceases,
the circulation of the blood is suspended, and a stop is put to all the
vital operations of the body. This state, which is termed Asphyxia,
usually comes on, in a warm-blooded animal, within ten minutes of
the time when the respiration is completely suspended ; thus affording
the most convincing proof of the importance of that function in the
Animal economy. In many cold-blooded tribes, a much longer sus-
pension may be borne with impunity; as also by warm-blooded ani-
mals, when the general activity of their functions is lowered in the
state of hybernation (§ 121). We shall now inquire into the sources
of the necessity for this interchange of oxygen and carbonic acid ;
and the mode in which the suspension of it acts upon the system at
large.

642. All Organized bodies, as already explained, are liable to con-
tinual decay, even whilst they are most actively engaged in perform-
ing the actions of Life ; and one of the chief products of that decay is

368 SOURCES OF EXCRETION OP CARBONIC ACID.

carbonic acid. A large quantity of this gas is set free, during the
decomposition of almost every kind of organized matter ; the carbon
of the substance being united with oxygen supplied by the air. Hence
we find, that the formation and liberation of carbonic acid go on with
great rapidity after death, both in the Plant and in the Animal ; and
that they take place also, to a very great extent, in the period that
often precedes the death of the body, during which a general decom-
position of the tissues is taking place. Thus in Plants, as soon as
they become unhealthy, the extrication of carbon in the form of car-
bonic acid takes place in greater amount than its fixation from the
carbonic acid of the atmosphere ; and the same change normally takes
place during the period that immediately precedes the annual fall of
the leaves, their tissue being no longer able to perform its proper
functions, and giving rise, by its incipient decay, to a large increase
in the quantity of carbonic acid set free. The same thing happens
in the Animal body, during the progress of many diseases which are
attended with an unusual tendency to decomposition in the solids and
fluids, — such as eruptive fevers : — the quantity of carbonic acid set
free in Respiration is greatly increased, although the body remains
completely at rest ; and notwithstanding this, the blood frequently ex-
hibits an unusually dark hue, indicating that it has not been properly
freed from the unusual amount of that substance, which it has received
from the tissues.

643. Hence, the first object of the Respiratory process, which is
common to all forms of Organized being, is to extricate from the body
the carbonic acid, which is one of the products of the continual decom-
position of its tissues. The softness of many of the tissues of Animals,
and the large quantity of fluid contained in their bodies, render them
more prone than plants to this kind of decomposition ; and, in warm-
blooded animals, the higher temperature at which the fabric is usually
maintained, adds considerably to the degree of this tendency; so that
the waste of their tissues, from this cause alone, is as much greater
than that of cold-blooded animals as the latter is than that of Plants.
But when the temperature of the Reptile is raised by external heat to
the level of that of the Mammal, its need for respiration increases,
owing to the augmented waste of its tissues. When, on the other
hand, the warm-blooded Mammal is reduced, in the state of hyberna-
tion, to the level of the cold-blooded Reptile, the waste of its tissues
diminishes to such an extent, as to require but a very small exertion of
the respiratory process to get rid of the carbonic acid, which is one of
its chief products. And in those animals which are capable of retain-
ing their vitality when frozen (§ 136), or when their tissues are com-
pletely dried up (§ 159), the decomposition is, for the time, entirely
suspended, and consequently there is no carbonic acid to be set free.

644. But another source of Carbonic acid to be set free by the Re-
spiratory process, and one which is peculiar to Animals, consists in the
rapid changes which take place in the Muscular and Nervous tissues,
during the period of their activity. It has been already shown (§ 361),

SOURCES OF EXCRETION OF CARBONIC ACID. 369

that there is strong reason to believe the waste or decomposition of
the Muscular tissue to be in exact proportion to the degree in which it
is exerted ; every development of muscular force being accompanied
by a change in the condition of a certain amount of tissue. In order
that this change may take place, the presence of Oxygen is essential ;
and one of the products of the union of oxygen with the elements of
muscular fibre is carbonic acid. The same may probably be said of
the Nervous tissue (§ 384). Hence it may be stated as a general
principle, that the peculiar waste of the Muscular and Nervous sub-
stances, which is a condition of their functional activity, and which is
altogether distinct from the general slow decay that is common to these
tissues with others, is another source of the carbonic acid which is set
free from the animal body ; and that the amount thus generated will
consequently depend upon the degree in which these tissues are exer-
cised. In animals which are chiefly made up of the organs of vege-
tative life, in whose bodies the nervous and muscular tissues form but
a very small part, and in whose tranquil plant-like existence there is
but very little demand upon the exercise of these structures, the quan-
tity of carbonic acid thus liberated will be extremely small. On the
other hand, in animals whose bodies are chiefly composed of muscle,
and whose life is an almost ceaseless round of exertion, the quantity
of carbonic acid thus liberated is very considerable.

645. We are enabled to trace the connection between the amount
of muscular exertion, and the quantity of carbonic acid set free in the
act of respiration, in the class of Insects, better than in any other.
They have no fi3j:ed temperature to maintain: and they are, conse-
quently, not in the condition of warm-blooded animals, in which the
quantity of carbonic acid set free is kept up to a more regular standard
by the provision to be presently noticed. On the other hand, they are
pre-eminent among all Animals, in regard to the energy of their mus-
cular power in relation to the bulk of their bodies; and the waste of
muscular tissue during their state of activity must therefore be very
great. Thus, a Humble Bee has been found to produce one-third of a
cubic inch of carbonic acid in the course of a single hour, during which
its whole body was in a state of constant movement, from the ex-
citement consequent upon its capture ; and yet during the whole
twenty-four hours of the succeeding day, which it passed in a state of
comparative rest, the quantity of carbonic acid generated by it was
absolutely less.

646. Besides these sources of Carbonic acid, which are common to
all Animals, there is another, which appears to be peculiar to the two
highest classes, Birds and Mammals. These are capable of maintain-
ing a constantly elevated temperature, as long as they are supplied
with a proper amount of appropriate food ; and their power of doing
so appears to depend upon the direct combination of certain elements
of the food, with the oxygen of the air, by a process analogous to com-
bustion ; these elements having been introduced into the blood for that
purpose, but not having formed a part of any of the solid tissues of the

24

370 SOURCES OF EXCRETION OF CARBONIC ACID.

body, unless they have been deposited in the form of fat. The nature
of these substances has been already noticed (§ 430). It is quite
clear that they cannot be applied in their original form, to the nutri-
tion of the tissues that originate in proteine-compounds; and it is tole-
rably certain that in the ordinary condition of the body, they undergo
no such conversion as would adapt them to that purpose. The Liver
seems to afford a channel, by which some of the fatty matters are
drawn off from the blood; but even these seem, in part at least, to be
re-absorbed (§ 725), and to be thrown off by the respiratory process.

647. The quantity of carbonic acid that is generated directly from
the elements of the food, seems to vary considerably in different ani-
mals, and in different states of the same individual. In the Carnivo-
rous tribes, which spend the greater part of their time in a state of
activity, it is probable that the quantity which is generated by the
waste or metamorphosis of the tissues is sufficient for the maintenance
of the required temperature, — and that little or none of the carbonic
acid set free in respiration is derived from the direct combustion of
the materials of the food. But in Herbivorous animals of compara-
tively inert habits, the amount of metamorphosis of the tissues is far
from being sufficient; and a large part of the food, consisting as it
does of substances that cannot be applied to the nutrition of the tis-
sues, is made to enter into direct combination with the oxygen of the
air, and thus to compensate for the deficiency. In Man and other
animals, which can sustain considerable variations of climate, and
can adapt themselves to a great diversity of habits, the quantity of
carbonic acid formed by the direct combination of the elements of the
food with the oxygen of the air, will differ extremely under different
circumstances. It will serve as the complement of that which is formed
in other ways ; so that it will diminish with the increase, and will
increase with the diminution, of muscular activity. On the other
hand, it will vary in accordance with the external temperature ; in-
creasing with its diminution, as more heat must then be generated ;
and diminishing with its increase. — In all cases, if a sufficient supply
of food be not furnished, the store of fat is drawn upon ; and if this
be exhausted, the animal dies of cold (§ 117).

648. To recapitulate, then ; the sources of carbonic acid in the Ani-
mal body are threefold. — 1. The continual decay of the tissues; which
is common to all organized bodies ; which is diminished by cold and
dryness, and increased by warmth and moisture ; which takes place
with increased rapidity at the approach of death, whether this affect
the body at large, or only an individual part; and which goes on un-
checked, when the actions of nutrition have ceased altogether. — 2.
The m.etamorphosis, which is peculiar to the Nervous and Muscular
tissues ; which is the very condition of their activity ; and which
therefore bears a direct relation to the degree in which they are ex-
erted.— 3. The direct conversion of the carbon of the food into car-
bonic acid ; which is peculiar to warm-blooded animals ; and which

NATURE OF THE RESPIRATORY PROCESS. 371

seems to vary in quantity, in accordance with the amount of heat to
be generated.

649. Now the function of Respiration has for its object, not merely
to extricate the carbonic acid, which is generated in the system ; but
likewise to introduce the oxygen, which is required to form that car-
bonic acid ; — the proportion of oxygen in the tissues, and in the com-
bustible materials of the blood, not being sufficient for this purpose.
Hence it is not enough, that the carbonic acid should be removed;
for this may be accomplished by causing an animal to breathe an
atmosphere which contains no oxygen. Any cold-blooded animal,
such as a Frog or a Snail, may be kept in hydrogen or nitrogen for
several hours or even days ; and will give out, during that time, an
amount of carbonic acid nearly as great as if it had been respiring
atmospheric air. But the continued production of carbonic acid must
have a limit, occasioned by the want of oxygen, and death will then
supervene. — On the other hand, a supply of oxygen may be freely
afforded ; and yet the presence of even a small amount of carbonic
acid in the surrounding atmosphere (in addition to that which is nor-
mally present in it, § 81) will impede the extrication of that substance
from the blood ; and if the excess be considerable, the carbonic acid
will not be set free at all ; so that the same injurious results follow,
as if respiration were altogether prevented from taking place.

650. These two actions are accomplished by the very same act ;
advantage being taken of the property of '' mutual diffusion," which
is common to all gaseous substances that do not unite chemically with
one another. In virtue of this property. Hydrogen, the lightest of
gases, and Carbonic acid, one of the heaviest, when introduced into
the same vessel, will be found in a short time to have uniformly mixed,
notwithstanding the difference of their specific gravities, which are as
1 to 22. Now this intermixture will take place, when the two gases
are separated by a porous septum; each gas passing towards the other,
by an action resembling the Endosmose and Exosmose of liquids
(§ 491). And it may also take place, when one of the gases is dif-
fused through a liquid ; provided that the other gas is likewise
capable of being absorbed by the liquid. In this manner, as already
mentioned, the surface of venous blood, inclosed in a bladder, may
be made to exhibit the arterial hue, by suspending the bladder in an
atmosphere of oxygen ; for the carbonic acid of the blood, and the
surrounding oxygen, will overcome by their mutual attraction the ob-
stacle interposed by the bladder ; and the former will be lifted out,
so to speak, and will be replaced by the latter. It has been found by
experiment, that the free carbonic acid diffused through blood, may be
more completely extricated from the liquid, by exposing it to hydrogen,
than by placing it under the vacuum of an air-pump ; for in the latter
case there is nothing to replace it, and the attraction between the gas
and the liquid tends to resist the exhausting influence of the vacuum;
whilst in the former, the blood receives one gas in exchange for the

372 ESSENTIAL STRUCTURE OF RESPIRATORY ORGANS.

other, so that the whole force of the tendency to mutual diffusion is
exercised in lifting out the carbonic acid.

651. The immediate purpose of the organs of Respiration, then, —
whatever may be the variety in their form, — is this : to expose the
blood to the air, in a state of such minute division as to present a very
extended surface, a thin membrane only being interposed between
them. For this purpose we find a certain organ, or set of organs,
specially set apart in all the higher animals ; and this is formed by a
prolongation of the general surface, either externallv or internally,
according to the mode in which the respiration is accomplished. Thus
in Fishes and aquatic Mollusks, the blood is aerated by exposure, not
directly to the atmosphere, but to the air which is dissolved in the
water they inhabit ; and the respiratory apparatus is formed in them
of an extension of the external surface, at a particular part, into innu-
merable delicate fringe-like

^^g-^- processes, the gills (Fig. 96);

every division of which con-
tains a network of blood-
vessels (Fig. 100) : so that
the amount of blood, which
is exposed to the surrounding
medium at any one time, is

collectively very great, al-

Doris johnstoni, showing the tuft of external gills. though the quantity Contained

in each gill-filament is very
minute. On the other hand, in all the air-breathing Vertebrata, the
blood is exposed to the atmosphere, through the medium of aninternal
membranous prolongation, which is continuous with the mucous mem-
brane lining the mouth and nostrils ; this forms a pair of sacs, termed
lungs, communicating with the back of the mouth by means of a tube
called the trachea or windpipe, through which air is freely admitted
to the cavities thus formed (Fig. 101). The blood is minutely dis-
tributed on the walls of these sacs by a close network of capillary
vessels (Fig. 102) ; and not only on the external walls, but also on
numerous partitions, by which the cavities are subdivided with more
or less minuteness, so as greatly to extend the vascular surface.

652. Such is the essential nature of the Respiratory apparatus ; but
in order that it may be carried into the vigorous operation, which is
required in the higher classes of animals, various supplementary
arrangements are made, for the purpose of promoting the due influence
of the air upon the blood. In the first place, the capillary vessels of
the respiratory surface are connected with arterial trunks, which issue
immediately from the heart, and which thus convey a constant stream
of blood from that organ ; whilst they give origin to venous trunks,
which terminate directly in the heart, and which are ready to con-
vey back to it the blood that has undergone aeration. Thus by the
energetic action of the heart, and by the force generated in the capil-
laries of the lungs (§ 598), a constant renewal is effected in the blood,

I

RESPIRATORY ORGANS IN MOLLUSKS. 373

■which is exposed to the air through the medium of these organs. On
the other hand, the renewal of the blood would be useless, unless a
fresh supply of air w^ere continually being introduced, and that which
had been vitiated, by the loss of its oxygen and the admixture of
carbonic acid, were removed ; and this is effected by a series of mus-
cular movements, which are adapted for the alternate expulsion of
the vitiated air from the lungs, and for the introduction of a fresh
supply of pure air from the atmosphere. These movements are kept
up by a certain part of the nervous system ; but they are not depend-
ent upon any exertion of the will, for they continue during profound
sleep, and in other states in which even consciousness is altogether
suspended.

2. Different forms of the Respiratory Apparatus in the lower Animals,

653. Before proceeding to consider, in more detail, the structure
and actions of the respiratory apparatus in Man, we may advan-
tageously glance at the mode in which this function is effected in the
lower animals. — In the lowest and simplest, which are inhabitants of
the water, we do not find any special apparatus for the aeration of the
fluids of the body ; this being accomplished by the exposure of them
to the surrounding medium, through the thin integument; and the
interchange of the layer of water (holding air in solution) in contact
with the aerating surface, is effected either by the general movement
of the body, or by the action oi cilia (§ 234), which produce the cur-
rents necessary for this purpose. Not unfrequently, the internal sur-
faces— such as the walls of the stomach and of other cavities, — seem
as much concerned in this function as the external, or even more so ;
these cavities being distended with water taken in through the mouth,
and this water being frequently renewed, by the ejection of that which
has been vitiated, and by the introduction of a fresh supply. This is
the case in the Sea Anemone, for example, and in many other Polypes ;
and there are certain higher forms of the same class, in which there is
a great dilatation of the pharynx, which seems peculiarly destined for
the aeration of the fluids, — being filled with water, and then suddenly
emptied, at tolerably regular intervals.

654. In the various classes of the Molluscous sub-kingdom, we
find the respiration provided for, by the adaptation of distinct organs
for the purpose. As most of the animals of this group are inhabi-
tants of the water, the respiration is usually carried on by means of
gills, rather than by any organs resembling lungs. The latter is found,
however, in a few species ; such as the Snail, Slug, and other terres-
trial air-breathing Mollusks ; and usually consists of a simple cavity,
situated in the back, communicating directly with the air through an
aperture in the skin, and having its walls covered with a minute net-
work of blood-vessels. The form and position of the gills differ
extremely in the several classes of Molluscous animals. In the lowest,
the respiratory surface is formed, as in the higher Polypes, by a dila-

374 RESPIRATORY ORGANS IN MOLLUSKS.

tation of the Pharynx ; but sometimes, instead of surrounding a large
cavity, it forms a special ribbon-like fold of membrane, passing from
one end of it to the other, on which the blood is minutely distributed.
In this group of animals, there is a regular system of canals for the
conveyance of the blood ; but these, in many parts of the system,
and especially on the respiratory membrane, do not seem to be fur-
nished with distinct walls, and are rather mere channels excavated in
the tissues. And the circulation is liable to a continual change in its
direction ; the blood being sometimes transmitted to the respiratory
surface hefore it proceeds to the body, and sometimes afler it has
traversed the other tissues (§ 557). The water in contact with the
respiratory surface is continually renewed by the action of the cilia,
with which it is thickly covered.

655. In certain other Mollusks inhabiting bivalve shells, we find
that the internal surface of the mantle or skin that lines the valves, is
the special organ of respiration ; the external water having free access
to these, by the separation of the skin along the edges of the valves,
so that it enters the cavity in which the viscera are lodged, and bathes
their exterior. But in most bivalve Mollusks, the internal surface of
the mantle is doubled (as it were) into four ribbon-like folds, which
are delicately fringed at their edges, and which have, in fact, the same
essential structure as the gills of higher animals (§ 663). To these
the blood is transmitted, when it has been rendered venous by tra-
versing the vessels of the body generally ; and in these it is exposed,
through a surface which is greatly extended by the minute division
of the fringes, to the action of water introduced from without, and
constantly renewed by ciliary action. In many of these animals, as
in the common Oyster, the two lobes of the mantle are so completely
separated, that the water can still enter freely between the valves ;
but in general, they are more or less united, so that the cavity in
which the gills lie is partially closed. There is always a provision,
however, for the free access of water from without, by means of two
apertures, one for its entrance and the other for its ejection; and in
certain species which burrow deeply in sand or mud, these apertures
are furnished with long tubes, or siphons, which convey the water
from nearer the entrance of the burrow, and carry it thither again.
In these, also, a continued flow of water over the respiratory surface
is maintained by the vibration of the cilia, with which they are
clothed.

656. The position of the gills, in the Mollusca of higher organiza-
tion, is extremely variable. Sometimes they are disposed upon the
external surface of the body, and form delicate leaf-like or arbores-
cent appendages (Fig. 97); whilst in other cases they are enclosed in
a special cavity or gill-chamber, to which water is freely admitted
from without ; a continual interchange being provided for, either by
ciliary action, or by muscular movements specially adapted for the
purpose. The blood is conveyed to them, after having become
venous in traversing the capillaries of the general system, by means

RESPIRATORY ORGANS IN WORMS AND CRUSTACEA.

375

Fig. 97.

One of the arborescent pro-
cesses, forming the gills of
Doris Johnstoni separated and
enlarged.

of large channels and sinuses excavated in the several parts of the
body (§ 556) ; and after being aerated in the gills, it returns to the
heart, to be again conveyed to the system. In the Cuttle-fish tribe,
there are supplementary hearts at the origin of
the branchial arteries, — or vessels that distri-
bute blood to the gills ; and these have evi-
dently for their purpose, to render the respira-
tory circulation more energetic, and thus to
increase the aeration of the blood, in the de-
gree required for the vigorous habits of these
animals, which present a remarkable contrast
to the sluggish inert character of the Mollusca
in general. — In these classes, taken as a whole,
the respiration is low in its amount. The
blood contains no red corpuscles, excepting
perhaps in the highest class; and the change
in its composition, which is effected by the air,
is confined, therefore, to the fluid plasma, or
liquor sanguinis. And as it is not exposed
directly to the air, except in a few species, but to the air contained
in the water inhabited by the animals, this change cannot be very
energetically performed. But as the life of these animals is chiefly
vegetative, — as their movements, except in the highest classes, are
few and feeble, — and as they maintain no independent heat, — there
is but little need of the interchange, which it is the object of the re-
spiratory process to effect ; and these animals can sustain the complete
suspension of it for a long time.

657. Among many of the Articulated tribes, the respiration is car-
ried on upon a similar plan. In some of the lowest, such as the Tape-
worm of the intestinal canal, there is no special provision for the
aeration of the fluids ; the soft integument permitting the extrication
of carbonic acid, and imbibition of oxygen, in the required degree.
This is but very small, however ; the life of these animals being
almost purely vegetative. In the Marine Worms, which constitute a
numerous and interesting group, endowed with considerable loco-
motive powers, and leading a life of almost constant activity, there is,
on the other hand, a special provision for this function ; the blood
being transmitted, in the course of its circulation, to a series of gill-
tufts, which are composed of a delicate membrane prolonged from the
external surface of the body, and which sometimes have the form of
branching trees, and sometimes of delicate brushes made up of a bun-
dle of distinct filaments. In either case, the filaments are traversed
by blood-vessels, and are adapted to bring the blood into close rela-
tion with the surrounding water ; and the continual interchange of
the latter is provided for by the restless movements of the body.
The tufts are sometimes arranged along every segment of the body ;
and their multiplication prevents them from individually attaining any
considerable size. In other cases, they are disposed at intervals;

376

RESPIRATORY ORGANS IN CRUSTACEA AND INSECTS.

and they are then larger, being less numerous. Their most beautiful
development is where they are present on the head only, the rest of
the body being enclosed in a shelly or sandy tube, as in the Serpiila
and Terehellce. The gill-tufts then frequently present the appearance
of a flower, endowed, when alive, with the most brilliant and delicate
hues. In many animals of this group, there is a small supplementary
heart at the base of every one of the vessels, that distribute the blood
to the gills ; and this is obviously designed to aid in the respiratory
circulation, for which the feeble action of the dorsal vessel w6uld
not furnish sufficient power (§ 552).

658. The higher Articulated classes are, for the most part, adapted
to atmospheric respiration, on the plan to be presently explained ;
but there is one class, that of Crustacea, whose respiration is still
carried on through the medium of water. In the lowest forms of this
group, there is no special respiratory apparatus ; the general surface
being soft enough to admit of the required aeration of the fluids
through its own substance, and the animal functions being performed
with so little activity, that a very small amount of interchange is
required. In the higher orders, however, whose bodies are encased
within a hard envelop, we find external gills, like those of many
Mollusks ; and these are attached to the most movable parts of the
body, — one or more pairs of legs being in some instances kept in con-
stant agitation, for the purpose of producing currents in the surround-
ing fluid, that may serve for the aeration of the blood. In the Crab-
tribe, which constitutes the highest family of this class, the gills are
themselves enclosed within a cavity, formed by a sort of doubling of
the hard integument of the under side of the body ; and a constant
stream of water is maintained through this, by means of a peculiar
valve, situated in the exit-pipe ; the continual movement of the valve
causing a regular stream of water to issue from the gill-chamber, and
thus occasioning the entrance of a constantly fresh supply. In these,
also, we find a dilatation, the walls of which seem to have contractile
powers, at the commencement of each artery that distributes the
blood to the gills ; and this collects the venous blood from the various
channels, in which it has meandered through the body. It is by the
enclosure of the gills within a cavity, and by the consequent protec-
tion of them from the drying influence of the air (which would prevent
their function from being duly performed), that Crabs and other allied
species are enabled to live for a considerable time out of water ; and
the Land-Crabs, as they are termed, are adapted to spend the greater
part of their lives at a distance from the sea, by means of a special
glandular apparatus within the gill-cavity, which secretes a fluid that
preserves the surface of the gills in the moist condition, requisite for
the aeration of the blood through its membrane. Thus the Land-
Crabs are air-breathing animals (except at certain seasons, when they
frequent the sea-shores), although they breathe by gills.

659. In Insects and other proper air-breathing Articulata, however,
the character of the respiratory apparatus is very diflferent. The transi-

RESPIRATORY ORGANS IN INSECTS.

377

tion from one form to the other is effected through such animals as
the Leech and the Earthworm, which seem able to breathe either air
or water. These are furnished with a series of small sacs, disposed
at regular intervals along each side of the body, and opening by a
row of pores, which are termed spiracles or stigmata. The blood-
vessels are distributed upon the walls of these sacs ; and either air
or water may be introduced into their interior, by the movements of
the body, which ^re adapted to compress their walls, and then to
allow them to dilate. In the Centipedes and their allies, these air-
sacs send out prolongations; which have not, however, any very
ready communication with each Mher. But in insects, the spiracles,
instead of forming the en-
trances to so majiy distinct ^^^ Tig.ds. ^
sacs, open into a pair of large
tubes, one of which traverses
the body on either side,
along its whole length.
These tubes, termed ^racAets,
have many communications
with each other across the
body ; and they branch out
into innumerable prolonga-
tions, the ultimate ramifica-
tions of which are distributed
to every portion of the sys-
tem. They occasionally
present dilatations of con-
siderable size (Fig. 98, a.) ; especially in the thoracic region of the
body, in those insects, which are endowed with great powers of flight.
These dilatations or air-sacs appear destined to serve as reservoirs of
air, during the time that the insect is upon the wing, its spiracles
being then partially closed ; and they may also be useful in diminish-
ing the specific gravity of the body. The air-tubes are prevented
from having their cavity obliterated through the pressure of the sur-
rounding parts, by means of an elastic spiral fibre ; which winds
round them, between their outer and inner membrane, from one ex-
tremity to the other (Fig. 98, b.) ; and which answers the purpose of
the cartilaginous rings and plates, in the trachea and bronchi of air-
breathing Vertebrata.

660. In this manner, the air that is introduced through the spiracles
is carried into every part of the body, and is brought into immediate
relation with the tissues to be aerated ; so that the carbonic acid
which they set free is communicated at once to the atmosphere, in-
stead of being taken up by the blood ; and the oxygen they require is
imbibed in the same manner. And thus we see how the respiration
of this interesting class, which is unequaled for its energy when the
body is in a state of activity, is provided for without an active circu-
lation of blood, and without the presence of red corpuscles, — which

Respiratory apparatus of insects:— a, air vesicles and
part of tracheal system of Scolia hortorum. b, portion of
one of the great longitudinal tracheae of Carabus aurattis,
with one of its spiracles.

378 COMPARATIVE FORMS OF RESPIRATORY APPARATUS.

elsewhere seem to be essential conditions of the interchange of oxygen
and carbonic acid between the air and the tissues, wherever this takes
place to any great extent.

661. In the Spider tribe, w-e return to a more concentrated form of
the respiratory apparatus ; but, notwithstanding that it is limited
within much narrower dimensions externally, it exposes a very large
amount of surface on its interior. It consists of a series of sacs, much
less numerous than in the lower Articulata, and not communicating
with each other. Their lining membrane, however, is doubled into
a series of folds, which lie in proximity with each other, like the
leaves of a book, and which thus firesent a very extensive surface
wathin a very small space. Over this surface, the blood is distributed
in a minute capillary network ; and thus it comes into immediate re-
lation with the air, which is received into the cavity through its aper-
ture or spiracle. The alternate admission and expulsion of air seem
to be provided for, as in Insects, by movements of the body, which
first empty the cavities or air-tubes by compression, and then allow
them to be re-filled by their own elasticity, the pressure being relaxed.
The respiratory cavities in the Spider-tribe have received the name of
'pulmonary branchice ; from their analogy, on the one hand, with the
lungs of higher animals ; and, on the other, with the branchial or gill-
cavity of the higher Crustacea, the gills in which are formed by pro-
longations of the lining membrane, like the leaf-like folds in the air-
cavities of the Spider-tribe.

662. The accompanying diagram will give an idea of the relations of
these different forms of the respiratory apparatus, amongst themselves,
and to that of Vertebrata. Let the line a b represent the general

Fig. 99.

Diagram illustrating different forms of the Respiratory apparatus :— a, simple leaf-like gill ; b, simple
respiratory sac ; c, divided gill ; rf, divided sac ; e, pulmonary branchia of Spider.

surface of the animal ; the continuations of that line on its upper side
being its external prolongations; and those below, its internal pro-
longations or reflexions. Now at a is seen the character of the simple
foliaceous or leaf-like gill, such as is found in the lower aquatic ani-
mals ; presenting merely a flat expanded surface in contact with the
water, over which the blood may be distributed. At b is shown a
correspondingly simple inversion ; such as that which forms the re-
spiratory sac of the leech, having the blood-vessels distributed upon
its walls. A higher form of the gill, such as is found in fishes and

RESPIRATORY ORGANS OF FISHES. 379

in the higher aquatic Invertebrata, is seen at c; the surface being
greatly extended, by subdivision into minute filaments. A more
complex form of the pulmonary apparatus, such as is found in the
higher Vertebrata, is shown at d; the blood being distributed, not
merely to its outer walls, but to the minute partitions which subdivide
its cavity into cells. And at e is represented the respiratory organ of
the Spider-tribe ; which bears an obvious resemblance to the lung of
the Vertebrated animal, show^n at d ; whilst it is evidently as nearly
allied to the gill shown at c, provided this be imagined to be sunk
within a cavity formed by a depression of the external surface, instead
of projecting beyond it. — Thus we see how very close is the real
resemblance between all the forms of the respiratory apparatus ; how-
ever unlike each other they may at first sight appear to be.

663. The gills of Fishes correspond with those of the higher Mol-
lusca in all essential particulars; but they are more largely developed
in proportion to the size of the body ; and they are placed in a situa-
tion that enables them to receive a more regular and constantly-
changed supply, both of blood and water. The gills are suspended
to bony or cartilaginous arches, of which
three, four, or more, are fixed on either side Fig. loo.

of the neck ; and the fringes hang loosely
within a cavity, which communicates on the
one hand with the mouth, and on the other
with the exterior of the body. The mechan-
ism of respiration is very complex in these
animals; and is evidently adapted to produce
the most effectual aeration possible. The

mouth is first distended with water ; and its ^apniary network of a pair

muscles are then thrown into contraction, in of leaflets of the giiis of the

, . 1 ., i ii 1 Eel: — a, a, branches of the

such a manner as to expel the water, through branchial anery conveying

the aperture on either side of the pharynx, jrSranctaf \t'in!' retu^Sl
into the gill-cavity. At the same time, the atirated biood The disappear-

p i«^ 1 I 1 /. anceof the dark shading in the

bony arches are lifted and separated from network, as it traverses the

f ., 1 ii .' c ^ gi'l' is designed to indicate the

each other, by the action Ot muscles espe- change in the character of the
Cially adapted to this purpose; so that the Jloodas^^ passes from one side

gill-fringes may hang freely, and may present

no obstacle to the flow of the water between them. When they have
been thus bathed with the aerating liquid, and their blood has under-
gone the necessary change, the water is expelled through the out-
ward aperture on each side of the back of the neck ; which is fur-
nished with a large flap or valvular cover termed the operculum. In
some of the cartilaginous Fishes, each branchial arch is inclosed in a
separate cavity ; which communicates on the inner side with the pha-
rynx by an orifice peculiar to itself, and by another orifice with the
external surface. Thus there is a series of external openings, instead
of a single one, on each side of the neck; and these sometimes amount
to six or seven, as in the Lamprey, reminding us of the spiracles of
Articulated animals ; whilst there is a corresponding series of internal

380 RESPIRATORY ORGANS OF FISHES.

openings into the pharynx on either side, or into a tube that commu-
nicates with it.

664. It is well known, that most Fishes speedily die when removed
from the water ; and it can be easily shown, that the deficient aeration
of the blood is the immediate cause of their death. But as it might
have been expected, that the atmosphere would exert a much more
energetic influence upon the blood contained in the gills, than that
which is exercised by the air contained in the water, the question
naturally arises, how this deficient aeration comes to pass. It is
chiefly due to the two following causes ; the drying up of the mem-
brane of the gills themselves, where it is exposed to the air, so that
the aeration of the blood is impeded ; — anc^ the flapping together of
the filaments of the gills, which no longer hang loosely and apart, but
adhere in such a manner as to prevent the exposure of the greater
portion of their surface to the air. Those fishes live longest out of
water, in which the external gill-openings are very small, so that the
gill-cavity may be kept full of fluid ; and there are certain species
which are provided like the Land-crab, with a particular apparatus
for keeping the gills moist, and which perform long migrations over
land in search of food, even (it is said) ascending trees. These are
exceptions to the general rule.

665. The respiration of Fishes is much more energetic than that
of any of the lower aquatic animals ; and this is partly due to the
great extension of the surface of the gills, partly to the provision just
explained for maintaining a constant flow of fresh water over their
surface, and partly to the position of the heart at the base of the main
trunk that conveys the blood to the gills (§ 558), by which the regu-
lar propulsion of that fluid through these organs is secured. Their
blood, too, is furnished with red corpuscles; which give important
aid in conveying oxygen from the gills to the remote tissues of the
body, and in returning the carbonic acid to be excreted. The pro-
portion of these varies considerably, in the diflferent species of the
class, being very small in those that approach most nearly to the
Invertebrata ; and there is even an entire absence of them in one
remarkable fish, the Amphioxus or Lancelot ; whilst they are pre-
sent in large numbers in the blood of certain Fishes, which have
great muscular activity, and can maintain a high independent tem-
perature.

666. It would seem, however, that not even this high amount of
respiration is always suflficient for Fishes, which live in small col-
lections of water, where their temperature is liable to be greatly
augmented by the heat of summer ; under which condition, there is
an increased proneness to disintegration in their tissues, and a cor-
responding necessity for the extrication of carbonic acid and for the
absorption of oxygen. Many fresh-water fishes under such circum-
stances, may be seen to come to the surface and to swallow air ; and it
would seem as if the interior of the intestinal canal then served the
purpose of a respiratory surface, the air being expelled from the anus,

RESPIRATORY ORGANS OF FISHES AND REPTILES. 381

deprived of a large part of its oxygen, and highly charged with car-
bonic acid.

667. In addition to their apparatus for aquatic respiration, many
Fishes are provided, in their air-bladder^ with the rudiments of the
air-breathing apparatus of higher animals; although it is only in cer-
tain species, which approach Reptiles in their general organization,
that this really affords any aid in the aeration of the blood. The
air-bladder in its simplest condition is entirely closed ; and it is then
obviously incapable of taking any share in the respiratory function,
although it seems to be an organ of some importance to the animal, in
regulating its specific gravity, and altering its position in the water.
In other cases, it communicates with the intestinal tube by a short
wide canal, termed the ductus pneumaticus ; and this may serve to
admit air, which is taken into the alimentary tube by the process of
swallowing just mentioned. In the Sauroid Fishes, just adverted to,
the air-bladder forms a double sac, which is evidently the repre-
sentative of the double-lung of the air-breathing Vertebrata ; and it
communicates with the back of the mouth by a regular trachea or
windpipe, which has a muscular valve at its commencement, serving
to open or close its orifice. Some of these fishes are able to live for
a considerable time out of water, their respiration being maintained
by these rudimentary lungs ; and they can also make a hissing sound,
by the expulsion of the air-sacs through the narrow glottis, or entrance
to the trachea.

668. The condition of the Respiratory apparatus, and the mode in
which the function is performed, in the class of Reptiles, are peculiarly
interesting; as it is in this class, that we first meet with the complete
adaptation of the Vertebrated structure to the aeration of the blood by
the direct influence of the atmosphere. Their general habits of life
require but a very feeble amount of aeration, especially at moderate
temperatures ; their muscular and nervous systems being usually exer-
cised in a very low degree ; their movements being sluggish, and their
perceptions obtuse. In fact, they may be considered, on the whole,
as the most vegetative of all Vertebrated animals. In accordance
with this character, the lungs are so constructed, as not to expose any
very large amount of blood to the air at any one time; and, as we
have already seen (§ 563), only a portion of the stream of the circu-
lation is diverted to the lungs ; the main current being sent to the
system with only that amount of aeration, which it has derived from
the admixture of the portion of blood that has been aerated in the
lungs, with the venous current that has last been returned from the
system.

669. The lungs of Reptiles are, for the most part, capacious sacs,
occupying a considerable part of the cavity of the trunk; but they are
very slightly subdivided, so that the amount of surface they can
expose is really small. Where any subdivision exists, it is usually at
the upper extremity of the lung, near the point of entrance of the
bronchial tube ; and where there is no actual subdivision of the cavity,

382

RESPIRATORY ORGANS OF REPTILES.

Fig. 101.

Section of the Lung of the Turtle.

we usually find that its surface is extended in this situation, by the
formation of a number of little depressions or pouches in its walls,
upon which the blood-vessels are minutely distributed. The greatest
amount of subdivision is seen in the lungs of the Turtle tribe ; but

even in these, the partitions scarcely form a
complete division at any part of the lungs;
and the ultimate air-cells are of very large
size. The air-sacs of Reptiles are not filled,
like those of Mammalia, by an act of inspi-
ration, but by a process of swallowing,
which is comparatively tedious ; and, from
the small amount of aerating surface, in
proportion to the amount of air thus re-
ceived into the cavity, one inflation of the
air-sacs lasts for a considerable time. When
the replacement of oxygen by carbonic acid
has proceeded to an extent that renders the
air no longer fit to remain in the lungs, these
cavities are emptied by pressure exercised
upon them by the muscles of the trunk ; and
the slow exit of the air through the narrow
glottis is accompanied by a prolonged hiss-
ing sound, which is the only sort of voice
that is possessed by the greater part of the
Reptile class. The lungs are again filled by the swallowing-process ;
and all goes on as before.

670. Now in the Frog tribe, which forms the lowest order of Rep-
tiles (and which is sometimes ranked as a distinct class, under the
title of Amphibia), the respiration, during the early or Tadpole state,
is aquatic ; being carried on by means of gills, and conducted exactly
upon the plan of that of Fishes. The lungs are not developed, until
a period long subsequent to the animal's emersion from the egg;
and as soon as they are ready to come into play, an alteration begins
to take place in the circulating system, by which the current of blood
is diverted towards them, and away from the gills (§ 562). This
change takes place to its full extent in the Frog, Toad, Newt, and
their allies ; which henceforth have a respiration and a circulation
exactly analogous to that of Reptiles in general ; but it is checked
in the Proteus, Siren, and other species, which form the perenni-
branchiate group, — so called from the persistent character of their
gills, which still remain in action, the lungs never being sufficiently
developed to maintain the respiration by themselves. The curious
influence which Light possesses on this metamorphosis, has been
already referred to (§ 95).

671. This order Batrachia is further distinguished from other Rep-
tiles, even when the metamorphosis is complete, by the softness and
nakedness of the skin ; which is destitute of the scales and horny
plates, that cover it in the Lizards, Serpents, and Tortoises. The

RESPIRATION IN REPTILES AND BIRDS. 383

skin of the Frog tribe is a very important organ of respiration; being
richly supplied with blood-vessels; and exposing their contents to the
influence of the air, under circumstances nearly as favourable as those
afforded by the imperfectly-developed lungs of these animals. Thus a
Frog, from which the lungs have been removed, will live a consider-
able time at a moderate temperature, if its skin be freely exposed to
a moist air ; for in consequence of the peculiar mode in which the
circulation is carried on in these animals (§ 562), the interruption to
the flow of blood through the lungs does not (as in the higher classes)
produce a stagnation of the general current through the body; and the
blood receives, in its course through the skin, a sufficient amount of
aeration for the support of life. Indeed at a low temperature, the
influence of water on the skin is sufficient (by means of the air
included in the liquid) to remove the small amount of carbonic acid
then ready for excretion, and to supply the requisite amount of
oxygen; and Frogs may thus live beneath the water for any length of
time, without coming to the surface to breathe. But with the rise of
the temperature of their bodies, their blood requires a higher degree
of aeration ; and they then come to the surface to take in air by the
mouth, w^hich aerates the blood through the lungs. It appears that,
during the heat of summer, the pulmonary respiration, and the influ-
ence of the water on the skin, are not sufficient; as it is found that
Frogs die, if they are confined to the water under such circumstances,
— their natural habit being to quit the water at such times, so that the
air may exert its full influence on their skin as well as on their lungs.
They do not, however, quit the neighbourhood of water, and soon
die if exposed to a dry atmosphere ; for if the skin become dry, its
aerating function can be no longer performed. The same result
happens, if the passage of gases through the skin be impeded by
smearing it over with any unctuous substance. We shall presently
find reason to believe, that this cutaneous respiration is a very im-
portant part of the function, even in Man and the Mammalia.

672. The class of Birds presents a most striking contrast to that of
Reptiles, in regard to the energy of the respiratory function, and the
extent of the apparatus destined to its performance. The lungs in
these animals undergo a minute subdivision ; so that the extent of
surface, over which they expose the blood to the air, is greatly in-
creased. But this subdivision is not carried to the same degree of
minuteness as it is in Mammalia ; and the required extent of surface
would not be afforded by the lungs alone. In addition to these organs,
we find large air-sacs, communicating with them, disposed in different
parts of the body, — such as the abdominal cavity, the interspaces
among the muscles, the spaces between the muscles and the skin, &c.
These very greatly increase the respiratory surface ; their lining mem-
brane being extremely vascular, and adapted to expose the blood to
the influence of the air. In most Birds, the bones themselves are
hollow ; and the lining membrane of their cavities serves as an addi-
tional aerating surface, the air being introduced into the interior of

384 RESPIRATION IN BIRDS.

the bones, by canals that communicate directly with the lungs. So
free is this communication, that the respiration has been known to be
maintained through the fractured humerus of an Albatross, w^hen an
attempt was made to destroy the bird by compressing its trachea.
Thus the respiratory surface is extended into the remoter parts of the
system, very much as in Insects ; and the hollowness of the bones,
together with the presence of numerous air-sacs in different parts of
the body, contribute to diminish its specific gravity. The large quan-
tity of air thus included in different portions of the frame, also serves,
like that contained in the air-sacs of Insects, as a reservoir for the
supply of the principal aerating organs during active flight, when the
respiratory movements are less free.

673. The mechanism of Respiration in Birds is very different from
that w^hich produces the respiratory movements in Mammalia. The
cavities of the chest and thorax are not yet separated by a diaphragm ;
except in a very small number of species, that approach most nearly
to the next class. But, on the other hand, the w^hole cavity of the
trunk is more completely enclosed in a bony casing; the ribs being
connected with the sternum by osseous prolongations from the latter,
instead of by cartilages; and the sternum itself being so largely de-
veloped, as to cover almost the entire front of the body. Now the
natural condition of this bony framework is such, that when no pres-
sure is made upon it, the cavity it encloses is in a state of distension ;
and the state of emptiness can only be produced by a forcible com-
pression of the framework, through an exertion of muscular power.
The lungs, instead of being freely suspended in the cavity of the
chest, as in Mammalia, are attached to the ribs ; and their own tissue
is endowed with a degree of elasticity, which causes them to dilate
when they are permitted to do so. In the state of distension, there-
fore, which is natural to the cavity of the trunk, the lungs are ex-
panded, and fill themselves with air, which they draw in through the
trachea; and this condition they retain, until, by the action of the
external muscles upon the bony framework, the cavity of the trunk is
diminished, and the air is expelled from the lungs and air-sacs, which
are again filled as soon as the pressure is taken off. — As the air-sacs
chiefly communicate with the part of the lungs that is most distant
from the trachea, the air has to traverse the whole extent of these last
organs, both when it is being drawn into the air-sacs, and w^hen it is
being expelled from them ; so that it is made to serve for the aeration
of the blood in the most effectual manner.

674. Thus, although the respiratory apparatus of Birds does not
possess the highly-concentrated development, which we shall find it
to present in Mammals, it serves, by the extension of the aerating
surface through the body, to bring the air and the blood into most
intimate relation ; and the energy of the function is further provided
for, by the mode in which the pulmonary circulation is carried on (a
distinct heart, as it were, being provided for it, § 564), as well as by
the arrangement of the blood-vessels, which transmit to the respira-

1

RESPIRATION IN BIRDS AND MAMMALS. 385

tory organs the whole of the blood, that has been returned in a car-
bonated state by the great veins of the system. The very large pro-
portion of red corpuscles contained in the blood, gives additional
effect to these provisions. The very high amount of respiration which
is natural to Birds, and which cannot be suspended even for a short
time without fatal consequences, has a direct relation (as already
explained) with their extraordinary muscular activity ; and with the
high bodily temperature, which they are fitted to maintain, and which
cannot be lowered in any great degree without the suspension of their
other functions. Birds are peculiarly susceptible of impurities in the
atmosphere; and it has been shown by experiment, that if a Bird, a
Mammal, and a Reptile, be placed together in a liaiited quantity of
air, which gradually becomes vitiated by their respiration, the Bird
will die first, the Mammal next, and the Reptile last. Or if the Bird
be placed alone in a limited quantity of air, and be left until the
atmosphere is so vitiated as to be no longer capable of supporting its
life, a Mammal will still live for a time in that atmosphere ; and when
it is no longer fit to sustain the life of the Mammal, the Reptile may
still breathe it without injury for a considerable period. There is
strong reason to believe, indeed, that in former epochs of the Earth's
history, when the Reptile class was predominant, supplying the place
of Mammals on land, and of Birds in the air, the atmosphere was so
highly charged with carbonic acid, as not to be capable of sustaining
the life of the higher air-breathing Vertebrata.

3. Mechanism of Respiration in Mammalia and in Man.

675. It is in the class of Mammalia, that we find the Respiratory
apparatus presenting its highest degree of concentration ; and the
arrangements for its action the most complete. The lungs are divided
into cavities of extreme minuteness ; so that the extent of surface
which they expose is enormously increased. These cavities, or air-
cells are all connected with the trachea, by means of the bronchial
tubes and their minute subdivisions ; but on account of the minute-
ness of these passages, a considerable force would be required to
inflate the air-cells with air, if their distension were to be accom-
plished by the propulsion of air through the trachea, as we have seen
to be the normal mode of inspiration in Reptiles. Moreover, if the
air were introduced in this manner, the air-cells would be the last por-
tions of the pulmonary structure that.would be distended by it ; as well
as the first to be emptied, when the air is forced out again by external
pressure. The mechanism of Respiration in Mammalia, however, is
so arranged, that the air is most effectually drawn into the lungs; in-
stead of being/orced into them; and the distension of the air-cells is
far more complete than it could be rendered in the latter method,
besides being accomplished in a much shorter time.

676. The general principle of the operation is this. The lungs are
suspended in a cavity that is completely closed ; being bounded above

25

386 MECHANISM OF RESPIRATION IN MAMMALS.

and around by the bony framework of the thorax, the interspaces of
■which are filled up by the muscles and membranes ; and being entirely
cut off from the abdomen below, by the diaphragm. Under ordinary
circumstances, the lungs completely fill the cavity; their external sur-
face, covered by the pleura, being everywhere in contact with the
pleural lining of the thorax. But the capacity of the thoracic cavity
is susceptible of being greatly altered by the movements of the ribs,
and by the actions of the diaphragm and abdominal muscles ; as will
presently be explained in more detail. When it is diminished, the
lungs are compressed, and a portion of the air contained in them is
expelled through the trachea. On the other hand, when it is increased
the elasticity of the air within the lungs causes them immediately to
dilate, so as to fill the vacuum that would otherwise exist in the tho-
racic cavity; and a rush of air takes place down the air-tubes, and
into the remotest air-cells, to equalize the density of the air they in-
clude (which has been rarefied by the dilatation of the containing
cavities) with that of the surrounding atmosphere.

677. The diameter of the ultimate air-cells of the Human lung varies
from about the l-200th to the l-70th of an inch. Their shape is
irregular ; and their walls are, for the most part, flattened against
each other. Each of the ultimate ramifications of the bronchial tubes
communicates with a cluster of these air-cells grouped around it;

those which are in immediate
F'&^^2. proximity wuth the tube open

into it by well-defined circular
apertures ; and the others com-
municate with it by opening
into these and into each other.
Each air-cell is lined by an
extension of the mucous mem-
brane from the bronchial tubes ;
and this is covered by a deli-
cate pavement-epithelium. Be-
tween the adjacent air-cells, is
a network of fibrous tissue,
that forms the connecting me-
dium by which they are held
th^uuSrCg"!^ '^' Capillaries of the air-cells of together ; this tissue appears to

be of the elastic kind. The
pulmonary arteries subdivide into branches, whose ultimate ramifica-
tions form an extremely minute capillary plexus; and this is disposed
between the walls of the adjacent air-cells, so that each portion of
this plexus comes into relation with the air (through the lining mem-
brane of the contiguous air-cells) on both sides, — an arrangement
which is obviously the most favourable that can be to the aeration of
the contained blood. It has been calculated by M. Rochoux, that
the number of air-cells grouped around each terminal bronchus is
little less than 18,000; and that the total number in the lungs amounts

i

I

STRUCTURE OF THE LUNGS IN MAN. 387

lo six hundred millions. If this estimate be even a remote approxi-
mation to the truth, it is evident that the amount of surface exposed
by the walls of these minute cavities, must be very many times greater
than that of the exterior of the body.

678. The larger bronchial tubes are more or less cartilaginous; but
the smaller branches do not possess any such deposit in their walls,
though still retaining their circular form. We find in the latter a
fibrous structure, which seems to possess the properties of non-striated
muscle ; and by this, the diameter of these tubes appears to be gov-
erned. The contractility of the walls of the smaller bronchi may be
excited by chemical, electrical, or mechanical stimuli applied to
themselves ; though it is not readily caused to manifest itself by sti-
mulating the nerves. By the continued influence of galvanism,
bronchial tubes of a line in diameter have been made to contract, until
their cavity was nearly obliterated. What purpose this contractility
may serve, during the ordinary actions of the lungs, it is not easy to
say ; but it manifests itself strongly in certain diseased conditions,
especially in Spasmodic Asthma, which appears essentially to consist
in a contracted state of the smaller bronchial passages, occasioning
an interruption to the passage of air through them. It is interesting
to observe, that the contractility of the muscular walls of these tubes
has been experimentally found to be greatly diminished by the appli-
cation of vegetable narcotics, especially stramonium and belladonna,
— substances which are well known to have a powerful remedial in-
flueiTce in spasmodic Asthma.

679. The Lungs themselves appear to be, almost entirely, passive
instruments of the Respiratory function. Their contraction when
over-distended, and their dilatation after extreme pressure, may be
partly due to the elasticity of their structure ; which seems to produce,
when acting by itself, a moderately distended state of the air-cavities.
This, too, is the condition that seems most natural to thecavity of the
chest; the fullest dilatation, or the most complete contraction, of
which it is capable, being only accomplished by a forcible eflfort.

680. The dilatation of the cavity of the chest, which constitutes
Inspiration, is accomplished by two sets of movements; — the elevation
of the ribs, — and the depression of the diaphragm. From the peculiar
mode in which the ribs are articulated w4th the spinal column at one
extremity, and from the angle which they make with the cartilages
that connect them to the sternum at the other, the act of elevatioft
tends to bring the ribs and the cartilages more into a straight line,
and to carry the former to a greater distance from the median plane of
the body, whilst the sternum is also thrown forwards. Consequently
the elevation of the ribs increases the capacity of the thorax, upw^ards,
forwards, and laterally. The movement is chiefly accomplished by
the Scaleni muscles, which draw up the first rib ; and by the Inter-
costals, which draw the other ribs into nearer proximity with each
other, so that the total amount of movement in each rib increases as
we pass from above downwards, — every one being drawn up by its

388 MECHANISM OF RESPIRATION IN MAN.

connection with the one above it, and being drawn nearer to it by the
action of its own intercostals. The elevation of the ribs is further
assisted by the serratus magnu§, and by other muscles connected with
the spine and the scapula ; and when the respiratory movement is very
forcibly performed, the scapula is itself drawn upwards, by the mus-
cles that descend to it from the neck, thus producing an increased
elevation of the ribs, and an unusual enlargement of the upper part
of the thoracic cavity. — When the respiratory action is to be per-
formed, the descent of the ribs is occasioned by the muscles of the
spine and abdomen, which proceed upwards from the lower part of
the trunk ; and this action is aided by the elasticity of the costal car-
tilages.

681. In the ordinary act of inspiration, however, the diaphragm
performs the most important part. The contraction of this muscle
changes its upper surface, from the high arch that it forms when re-
laxed and pushed upwards by .the viscera below, to a much more level
state ; though it never approaches very closely to a plane ; being
somewhat convex, even when the fullest inspiration has been taken.
When thus drawn down, it presses upon the abdominal viscera, and
causes them to project forwards, which they are allowed to do, by
the relaxation of the abdominal muscles. In tranquil breathing, this
action is alone nearly sufficient to produce the requisite enlargement
of the thoracic cavity ; the position of the ribs being very little altered.
In the expiratory movement, the diaphragm is altogether passive ;
for, being in a state of relaxation, it is forced upwards by the ab-
dominal viscera, which are pressed inwards by the contraction of
the abdominal muscles. These last, therefore, are the main instru-
ments of the expiratory movement ; diminishing the cavity of the chest
by elevating its floor, at the same time that they draw its bony frame-
work into a narrower compass.

682. In this manner, by the regularly alternating dilatation and
contraction of the thoracic cavity, the air within the lungs is alter-
nately increased and diminished in amount ; and thus a regular ex-
change is secured. This exchange, however, can only affect at any
one time a certain proportion of the air in the lungs; thus it is pro-
bable, that the quantity remaining in these organs after ordinary expi-
ration is above 100 cubic inches, whilst the amount usually expired
is not above 20 cubic inches. Indeed if it were not for the tendency
of gases to mutual diffusion, the air in the remote air-cells might
never be renewed. — If any aperture exist, by which air could obtain
direct access to the pleural cavity, the lungs would not be dilated by
its enlargement ; for the vacuum w^ould be supplied much more rea-
dily, by the direct ingress of the air (provided the aperture be large
enough), than by the distension of the lung. Thus a large penetrat-
ing wound of the thoracic cavity may completely throw out of use
the lung of that side; and the same result will follow, when an aper-
ture forms by ulceration in the substance of the lung itself, establish-
ing a free communication between the pleural cavity and one of the

MECHANISM OF RESPIRATION IN MAN. 389

bronchial tubes ; so that, of the air which rushes in by the trachea, to
compensate for the enlargement of the thoracic cavity, a great part
goes at once into that cavity, without contributing to the distension of
the lungs, and therefore without serving for the aeration of the blood.

683. The number of the respiratory movements (that is, of the acts
of inspiration and expiration taken together) may be probably esti-
mated at from 14 to 18 per minute, in a state of health and of repose
of body and mind. Of these, the greater part are moderate in amount,
involving little movement except in the diaphragm ; but a greater
exertion, attended with a decided elevation of the ribs, is usually
made at every fifth recurrence. The frequency of the respiratory
movements, however, is liable to be greatly increased by various
causes, such as violent muscular exertion, mental emotion, or quick-
ened circulation; whilst it may be diminished by torpidity of the
nervous centres, on which the movement depends, — as we see in
apoplexy, narcotic poisoning, &c. An acceleration seems very con-
stantly to take place in diseases, which unfit a part of the lung for the
performance of its function ; and the rate bears a proportion to the
amount thus thrown out of use. Thus, the usual proportion between
the respiratory movements and the pulse being as 1 to 4J or 5, it may
become in Pneumonia as 1 to 3, or even in severe cases as 1 to 2 ; the
increase in the number of respiratory movements being much greater
in proportion, than the augmentation of the rate of the pulse. But it
mus>t be remembered by the practitioner, that a simply hysterical state
may produce, in young females, an extraordinary acceleration of the
respiration ; the number of movements being sometimes no less than
100 per minute. There will be a great increase, also, in the number
of inspirations, when the regular movements are prevented from being
fully performed, by any cause that aflfects their mechanism, even whilst
the lungs themselves are quite sound. Thus in inflammation of the
pleura or pericardium, or in rheumatic aflfections of the intercostal
muscles, the full action of the ribs is prevented by the pain which the
movements produce ; and the same is the case in regard to the dia-
phragm, when the peritoneum or the abdominal viscera are affected
with inflammation. Under such circumstances, there is an involuntary
tendency to make up for the deficiency in the amount of the respira-
tory movements, by an increase in their number.

684. The combined actions of the respiratory muscles, which have
been now explained, belong to the group termed reflex; being the
result of the operation of a certain part of the nervous centres, which
does not involve the will, or even sensation, and which may continue
when all the other parts of the nervous centres have been removed.
In the Invertebrated Animals, we commonly find a distinct ganglionic
centre set apart for the performance of the respiratory movements ;
and the division of the nervous centres in Vertebrated animals, which
is the seat of the same function, may be clearly marked out, although
it is not so isolated from the rest. It is, in fact, that segment of the
medulla oblongata and upper part of the spinal cord, which is con-

390 MECHANISM OF RESPIRATION IN MAN.

nected with the 5th, 7th, and 8th pairs of cephalic nerves, and with
the phrenic. The entire brain may be removed from above (by suc-
cessive slicing), and the whole spinal cord may be destroyed below ;
and yet the respiratory movements of the diaphragm will still con-
tinue,— those of the intercostal and other muscles being of course
suspended, by the destruction of a portion of the cord, from which
their nerves arise. But if the spinal cord be divided, between the
point at which it receives the 5th and 8th pairs of nerves, and that
at which it gives origin to the phrenic, the movements of the dia-
phragm immediately cease ; and this is the reason why death is so
instantaneous, in cases of laxation or fracture of the higher cervical
vertebrsB, causing pressure upon the spinal cord just below its exit
from the cranium; whilst if the injury take place below the origin
of the phrenic nerve, life may be prolonged for some time.

685. The Respiratory movements, like other reflex actions (§ 394),
depend upon a stimulus of some kind, originating at the extremities
of the nerves, propagated towards the centre by the afferent trunks,
and giving rise to a motor impulse, which is transmitted along the
efferent or motor nerves to the muscles, and which occasions their
contraction. Now the importance of the respiratory function to the
maintenance of life, which has already been sufficiently pointed out,
necessitates an ample provision for its due performance; and thus we
find thatthe stimulus for theexcitementof the movements may be trans-
mitted through several channels. Its chief source, no doubt, is in the
lungs ; and arises from the presence of venous blood in the capillaries
and of carbonic acid in the air-cells. Under ordinary circumstances,
— that is, when the blood is being duly aerated, and the air being
properly renewed, — the impression thus made upon the nerves of the
lungs, is so faint, that we cannot perceive it, even when we specially
direct our attention to it. But if we suspend the movements for a
moment or two, we immediately experience a sensible uneasiness.
The ParVagum is obviously the channel, through which this impres-
sion is conveyed to the nervous centres ; and it is found that, if the
trunk of this nerve be divided on both sides, the respiratory move-
ments are greatly diminished in frequency. Hence it is undoubtedly
one of the principal excitors of the respiratory movements.

686. But the sensory nerves of the general surface, and more par-
ticularly the sensory portion of the Fifth pair, which supplies the face,
are most important auxiliaries, as excitor nerves ; the inspiratory
movement being peculiarly and forcibly excited by impressions made
upon them, especially by the contact of cold air or water with the
face. The power of the impression made by the air upon the gene-
ral surface, and particularly upon the face, in exciting the inspiratory
movement, is well seen in the case of the first inspiration of the new-
born infant, which appears to be excited solely in this manner. An
inspiratory effort is often made, as soon as the face has emerged from
the Vagina of the mother ; whilst, on the other hand, if the face be
prevented from coming into contact with cool air, the inspiratory

i

REFLEX CHARACTERS OF RESPIRATORY MOVEMENTS. 391

effort may be wanting. When it does not duly take place, it may
often be excited by a slap with the flat of the hand upon the nates
or abdomen ; a fact which shows the special influence of impres-
sions upon the general surface, in rousing the motor impulse in the
medulla oblongata, and in causing its transmission to the muscles.
The deep inspirations which follow a dash of cold water upon the
face, or the descent of the cold douche or of the divided streams of the
shower-bath upon the body, or the shock of immersion in the cold
plunge-bath, all testify to the powerful influence of such impressions
in the adult; and the efficacy of other kinds of irritation of the skin,
such as beating with holly twigs, in maintaining the respiratory move-
ments in cases of narcotic poisoning, shows that the required impres-
sions are not restricted to the contact of cold air or water. It seems
probable, from various facts, that the presence of venous blood in the
arterial capillaries of the system, and the consequent stagnation in the
current through them (§ 597), may exert an influence through the
Sympathetic system : which may be transmitted, by the copious inos-
culations of that system with the Par Vagum, to the Medulla Ob-
longata ; and which may there serve as a valuable auxiliary in excit-
ing the respiratory movements.

687. Of the mode in which the impressions, thus transmitted to
the Medulla Oblongata, act in exciting the motor impulses which
issue from it, nothing is known ; but these impulses, directed along
the phrenic, intercostal, and other nerves, produce the requisite move-
ments. When the stimulus is unusually strong, various nerves and
muscles are put in action, which do not co-operate in the ordinary
movements of inspiration ; and it may sometimes be observed, that
movements are thus excited in parts, which will not act in obedience
to the will, being to all appearance completely paralyzed. This fact
shows how completely the class of actions in question is independent
of the influence of the mind ; but we must not lose sight of the con-
trol which the mind, especially in the higher classes of animals, pos-
sesses over them. Various actions of the respiratory muscles, par-
ticularly those of weeping and laughing, are the most direct means of
expressing the passions and emotions of the mind ; and are invo-
luntarily excited by these. And, again, the respiratory actions are
placed to a certain degree under the control of the will ; in order
that they may be subservient to the production of vocal sounds, and
to the actions of speech, singing, &c. The will cannot long suspend
the respiratory movements ; for the stimulus to their involuntary per-
formance soon becomes too powerful to be any longer resisted. And
it is well that it should be so ; for if the performance of this most im-
portant function were left to our own choice, a few moments of for-
getfulness would be productive of fatal results. But it is to the power
which the will possesses, of directing and controlling the respiratory
movements, that we owe the faculty of producing articulate sounds,
and thus of holding the most direct and intimate converse with
each other.

392 INTERCHANGE OF OXYGEN AND CARBONIC ACID.

688. It is essential for the due performance of the respiratory move-
ments, that the portion of the nervous centres, on which they depend,
should be in a state of activity. This is the case, under ordinary
circumstances, throughout life. The state of perfect quiescence, to
which the brain is liable, never affects the medulla oblongata ; and
the respiratory movements are consequently kept up with as much
regularity and energy (in proportion to the requirements of the sys-
tem), during our sleeping, as during our waking hours. But if any
cause induce torpidity of the medulla oblongata, the respiratory move-
ments are then retarded, or even suspended altogether ; and all the
consequences of the cessation of the [aeration of the blood speedily
develop themselves (§ 706). This is seen in apoplexy; when the
pressure, or other cause of suspended activity, which at first affected
the brain alone, gradually propagates its influence downwards. The
same is the case in narcotic poisoning ; in which also the brain is the
first to be affected, and may suff*er alone ; but if the noxious influence
be propagated to the medulla oblongata, it manifests itself in the re-
tardation of the respiratory movements, and, when sufficiently power-
ful, in their complete suspension. Under such circumstances, it is
requisite to resort to all possible means of keeping up the respiratory
movements ; and when these fail, artificial respiration may be suc-
cessfully employed. For if, by such means, the circulation can be
prevented from failing for a sufficient length of time, the ordinary pro-
cesses of nutrition go on, the poisonous matter is gradually decom-
posed or eliminated by the secreting organs ; and the nervous centres
resume their usual functions. A torpid condition of the medulla
oblongata, inducing a retardation of the respiratory movements, seems
to be one of the morbid conditions attendant upon typhoid fever ; and
probably depends in the first instance upon a disordered state of the
blood, which does not exert its usual vivifying influence. In such
cases, the proportion of the respiratory movements to the pulse sinks
as low as 1 to 6, or even as 1 to 8 ; and thus the due aeration of the
blood is not performed, and its stimulating properties are still further
diminished.

4. Chemical Phenomena of Respiration,

689. Having now fully considered the means, by which the Atmo-
sphere and the blood are brought into relation in the lungs, we have
to examine into the results of their mutual action. It will be remem-
bered that the Atmosphere contains about 21 per cent, of Oxygen to
79 of Nitrogen, by measure ; or 23 parts of Oxygen to 77 of Nitro-
gen, by weight. The Nitrogen seems to perform no other part than
that of diluting the oxygen ; at least the results of the most recent and
exact experiments render it very doubtful, whether (in the respiration
of Man at least) any change is effected in the nitrogen of the inspired
air. The leading phenomenon of respiration, is the removal of a cer-
tain quantity of Oxygen from the air, and its replacement by Carbonic

AMOUNT OF CARBONIC ACID EXHALED. 393

acid. The relative proportions, which the oxygen absorbed, and the
carbonic acid exhaled, bear to one another, have been variously
stated. The most recent and trustworthy experiments on this subject
(those of Brunner and Valentin) lead to a very interesting result.
According to the law of the " mutual diffusion" of gases, the volumes
of any two gases, that pass through a porous medium to mingle with
each other, will be respectively in the inverse proportion to the square
roots of their specific gravities. Now when oxygen is on the outer
side, and carbonic acid on the inner, the volume of oxygen that
passes inwards will exceed that of the carbonic acid that passes out-
wards ; and this in the proportion of 1174 to 1000. This calculation,
deduced from the relative densities of the two gases, corresponds so
closely with the actual result of experiments upon the respiration of
Man, that it seems next to certain, that the interchange of oxygen and
carbonic acid, which occurs between the air and the blood in the
lungs, takes place in exact accordance with this law of mutual dif-
fusion.

690. Now Carbonic Acid contains precisely its own volume of
oxygen ; consequently, of the 1174 parts of oxygen absorbed, 1000
are excreted again by the lungs in the form of carbonic acid ; and
there remain 174, or nearly 15 per cent., to be accounted for in other
ways. It is certain that some of this enters into combination with the
sulphur and phosphorus of the original components of the body ; and
converts these into sulphuric and phosphoric acids ; and the remainder
must enter into other chemical combinations, very probably uniting
with the hydrogen of the fatty matter, to form part of the water
which is exhaled from the lungs.

691. It is difficult to form an exact estimate of the actual quantity
of Carbon, thrown off from the lungs in the form of Carbonic Acid
during any lengthened period ; since the amount disengaged during
experiments carried on for a limited time, cannot, for many reasons,
be taken as affording a fair average. Thus the quantity will vary with
the external temperature, with the state of previous rest or activity,
with the length of time that has elapsed since a meal, and particularly
with the general development of the body. The amount of carbonic
acid exhaled is greatly increased by external cold ; as is shown in
the results of such experiments as the following. Small Birds and
Mammals having been enclosed in a limited quantity of air, for the
space of an hour, at ordinary temperatures, the quantity of carbonic
acid they produced was noted. The experiment was then repeated. at
a temperature nearly approaching that of the body ; and was performed
a third time at a temperature of about 32°. The following are the
comparative amounts.

Temp. 590^680.

Temp 860—1060.

Temp, about 320.

Grammes.

Grammes.

Grammes.

A Canary

0-250

0-129

0-325

A Turtle-dove

0-684

0-366

0-974

Two Mice

0-498

0-268

0-531

A Guinea-pig

2-080

1-453

3006

394 AMOUNT OF CARBONIC ACID EXHALED.

Thus it would appear that the quantity of carbonic acid exhaled be-
tween 86° and 106° is not much more than half of that which is
exhaled between 59° and 68° ; and is only about two-fifths of that
which is given off at 32°.

692. The quantity of carbonic acid exhaled during exercise, and
for a certain time after it, and also after a full meal, is considerably
increased ; whilst on the other hand, it is greatly diminished during
sleep. Thus a person who was excreting 145 grains of carbon per
hour, whilst fasting and at rest, excreted 165 after dinner, and 190
after breakfast and a walk ; whilst he only excreted 100 during sleep.
The variation with the general development of the body, and also
with the sex and age, is considerable. Thus, the exhalation is almost
always greater in males than in females of the same age, at every
period of life except childhood. In males, the quantity increases
regularly from eight to thirty years of age, remaining nearly stationary
until forty ; — thus it averages 77*5 grains of carbon per hour at eight
years ; 135 grains at fifteen ; 176*7 grains at twenty ; and 189 grains
between thirty and forty. Between forty and fifty, there is a well-
marked diminution, the average being then 156 grains ; and the dimi-
nution continues up to extreme old age, when the amount exhaled
scarcely exceeds that which is extricated at ten years of age ; thus,
between sixty and eighty, it was 142*5 grains; and in a man of a
hundred and two, it was only 91*5 grains. These average results,
however, are widely departed from in individual cases ; an extraor-
dinary development of the muscular system being always accompanied
by a high rate of extrication of carbon ; and vice versa. Thus a man
of remarkable muscular vigour, whose age was twenty-six years,
exhaled 217 grains of carbon in an hour ; a robust man of sixty ex-
haled 209*4 grains ; and an old man of ninety-two, who in his
younger days had possessed uncommon muscular powers, and who
preserved a remarkable degree of energy, still consumed at the rate
of 151 grains per hour. On the other hand, a man of slight muscular
development, at the age of forty-five, only exhaled 132 grains; and
another at the age of seventy-six, only 92*4 grains.

693. Infemales, nearly the same proportional increase goes on, up
to the time of puberty ; when the quantity abruptly ceases to increase,
and remains stationary so long as menstruation continues regular. The
average quantity of carbonic acid exhaled by girls nearly approaching
puberty, is about 100 grains per hour ; and it remains at this standard
until nearly the close of menstrual life. At the period of the cessation
of the catamenia, it undergoes a perceptible increase; the average,
between forty and fifty years of age, being about 130 grains per hour ;
and the quantity exhaled in a woman of great muscular development,
and of forty- four years of age, rising to 152*4 grains in an hour. After
the age of fifty, or thereabouts, the quantity decreases, as in men. It
is remarkable that, during pregnancy, there is the same increase in the
exhalation of carbon, as there is after the final cessation of the cata-

AMOUNT OF CARBONIC ACID EXHALED. 395

menia ; and the same takes place, if the menstrual discharge be tem-
porarily suspended, through any other cause.

694. It is obviously difficult, then, to obtain exact estimates, from
any experiments conducted for a short time only, of the total amount
of carbon thrown off* during a lengthened period ; since the condition
of the individual varies so greatly at different times ; and the variation
amongst different individuals is so great. Moreover, of the total
amount of carbon excreted in a gaseous form, a certain part is un-
doubtedly set free from the skin ; and the proportion of this has not
been yet determined. As a means of measuring the whole quantity of
carbonic acid set free, without causing the respiratory movements to
be performed in any unnatural manner. Prof. Scharing constructed an
air-tight chamber, of dimensions sufficient to allow an individual to
remain in it for some time without inconvenience ; and so arranged,
that he could eat and drink, read, or sleep, within it. This was con-
nected with an apparatus, by which the air was continually renewed;
and the air drawn oflf was carefully analyzed in order to determine the
quantity of carbonic acid contained in it. The average per hour, in
different states, having been ascertained, it was calculated that, allow-
ing seven hours for sleep in adults, and nine hours for children, the
total amount of carbon consumed in the twenty-four hours was as
follows : —

No. Weighing. Grains. Oz. Troy.

1. A male, aged thirty-five, 131 lbs.

2. A male, aged sixteen, 115J lbs.

3. A soldier, aged twenty-eight, 164 lbs.

4. A girl, aged nineteen. 111 lbs.

5. A boy, aged nearly ten, 44 lbs.

6. A girl, aged ten, 46 lbs.

695. This estimate is perhaps rather too low ; as it does not take
sufficient account of the great increase, which is produced by exercise.
Another method has been adopted by Prof. Liebig; who endeavoured
to ascertain the total amount of carbon excreted from the body in the
form of carbonic acid, by comparing the amount of carbon taken in
as food, with that contained in the feces and urine ; the difference being
set down to the account of respiration. His estimate amounts to the
very large sum of 13*9 oz. of solid carbon per day, which he consi-
ders to be thus set free by the lungs and skin ; but this is almost cer-
tainly above the truth. The observations were made upon a body of
soldiers who were subjected to severe daily exertion ; and they were
far from being exactly conducted, many of the items being set down
by guess only, whilst of others no account whatever was taken. We
may perhaps consider 10 or 11 oz. as more nearly representing the
amount of carbon consumed by adult men exposed to severe exer-
tion ; whilst from Prof. Scharling's experiments it may be inferred,
that from 7 to 8 oz. of carbon are thrown off* during the twenty-four
hours by the lungs and skin of adult men not using much active exer-

3380

or

7-0

3450

or

7-2

3692

or

7-7

2555

or

5-3

2050

or

4-3

1938

or

4-0

396 AMOUNT OF CARBONIC ACID EXHALED.

tion ; to which another ounce or two may be added, as the increased
quantity excreted during moderate exercise. — On the other hand, from
experiments made upon the quantity of carbonic acid exhaled from
the lungs alone during a given time, it would appear that the pul-
monary excretion of carbon amounts to between b\ and 8 oz. in the
twenty-four hours ; and the difference may be partly set down to the
account of the cutaneous respiration.

696. If we assume 10 oz. or 4800 grains of solid carbon as the total
amount excreted from the lungs and skin of a male adult, using active
exercise in the course of twenty-four hours, w^e find that the volume
of carbonic acid thus generated must be nearly 37,000 cubic inches, or
more than 21 cubic feet. Of this about 16 cubic feet are probably
extricated from the lungs. But it is probable that about 10 cubic feet
per day is near the ordinary average. Now it has been ascertained,
that the whole quantity of air which passes through the chest during
that time under similar circumstances, is about 2QQ cubic feet; so that
the proportion of carbonic acid contained in the expired air seems to
average about 4 per cent. It is certain, however, that this proportion
may rise much higher ; particularly when the respiratory movements
are slowly and laboriously performed. Now in order that the blood
should be properly aerated, it is requisite that the air should contain
no previous impregnation of carbonic acid ; since the diffusion of even
a moderate per centage of that gas through the inspired air, seriously
impedes the exhalation of more. Thus it was found by Messrs. Allen
& Pepys, that when 300 cubic inches of air were respired for three
minutes, only 28J inches of carbonic acid (or somewhat more than 9
per cent.) were present in it; though the rate of its production in a
parallel experiment, in which fresh air was taken in at each inspira-
tion, w^as 32 cubic inches per minute, or 96 cubic inches in three
minutes. That it is not the deficiency of oxygen, but the presence of
carbonic acid in the inspired air, which impedes the free aeration of
the blood, is proved by the recent experiments of Dr. D. B. Reid ;
who has shown that an animal maybe kept alive in a limited quantity
of air, until nearly all its oxygen is exhausted, if an eff*ectual provi-
sion be made for drawing off'the carbonic acid as fast as it is generated.

697. An animal thus made to breathe an atmosphere, \diich con-
tains less than its normal proportion of oxygen, resembles one which
is made to breathe a rarefied atmosphere, such as that which exists on
the summits of high mountains. All persons who have made such
ascents, have experienced the insufficiency of rarefied air to sustain
the degree of respiration required for active exertion. As long as the
body remains at rest, no inconvenience is perceived ; but as soon as
the muscular system is put into action, the insufficiency of the supply
of oxygen is manifested by the feeling of distress and languor ; which
becomes so severe, that the individual, if unused to such ascents, is
obliged to stop and take breath at every few steps. The necessity
for doing so will be easily understood, when it is remembered that
when the pressure of the atmosphere is reduced to half its usual

CHANGES EFFECTED IN THE BLOOD. 397

amonnt, the hulk of a given weight of air will be twice as great as at
the surface of the earth, or the same measure will weigh only half as
much. Consequently, when the chest is completely filled with air,
the real quantity of oxygen included in it, is only half of that, which
is drawn in by a corresponding inspiration at the earth's surface.

698. Although an impregnation of carbonic acid, to the amount of
seven or eight per cent., would be required to destroy life in most
warm-blooded animals, yet a much smaller proportion is sufficient to
produce very injurious results. Thus the discomforts occasioned by
the presence of a crowded audience in a church, lecture-room, or
theatre, w^hich is not provided with sufficient ventilation, are due in
great part to the continued respiration of air, which becomes loaded
in the course of an hour or two with carbonic acid gas, to the amount
of from one-half to two per cent., — as has been ascertained both by
direct experiment, and by calculation. And there can be little doubt,
that the habitual respiration of such air, in the narrow and noisome
dwellings of the poor, or in crowded factories and workshops, has a
tendency to produce, both directly and indirectly, much loss of phy-
sical and mental vigour, and also to blunt the acuteness of the moral
feelings.

699. Having thus considered the changes produced by the Respi-
ratory function, in the air submitted to it, we have next to inquire
into converse series of change effected by it in the blood. The nature
of these cannot be well stated with precision ; as they have not yet
been fully determined. It was formerly supposed, that the venous
blood arrives at the lungs charged with carbon; and that this carbon
is united with the oxygen of the air, in the lungs themselves. Nu-
merous facts, however, go to prove, that the blood comes to the lungs
charged with carbonic acid; and that it gives out this ready formed,
and receives oxygen in its stead. Thus it has been already shown,
that there is a positive disappearance of oxygen ; more of that element
being withdrawn from the atmosphere, than is restored to it in the
condition of carbonic acid ; so that we know that the surplus must
be received into the blood. Moreover, the quantity of oxygen ab-
sorbed exactly replaces the quantity of carbonic acid set free, accord-
ing to the law of " mutual diffusion;" which could scarcely be the
case, unless the latter were contained in the blood already formed.
Further, cold-blooded animals may be made to breathe nitrogen or
hydrogen for a sufficient length of time, to cause a large quantity of
carbonic acid to be disengaged; and this must have been brought to
the lungs ready formed, since no oxygen was present there to gene-
rate it. Lastly, it can be shown by experiment, that oxygen, carbo-
nic acid, and nitrogen exist in a free state in blood, arterial as well
as venous ; but that the proportion of oxygen is greater in arterial than
in venous blood, whilst that of carbonic acid is less. The following
table expresses the per centage of each kind of gas in the two sorts
of blood respectively ; as deduced from the experiments of Magnus.

Arterial Blood.

Venous Blood

62-3

71-6

23-2

15-3

14-5

131

398 EXHALATION OF WATER FROM THE LUNGS.

Carbonic acid .

Oxygen ....

Nitrogen ....

Thus it appears that the quantity of nitrogen is very nearly the same
in both, as would be anticipated from what has been already stated in
regard to its non-participation in the respiratory process; whilst about
one-third of the free oxygen of arterial blood disappears during its cir-
culation in the systemic capillaries, to be replaced by an equivalent
amount of carbonic acid ; and a converse change takes place in the
pulmonary capillaries, this additional portion of free carbonic acid
being set free, and replaced by oxygen.

700. Thus it is evident, that a part of the change effected in the
blood consists in an alteration in the proportion of the gases which
always exist in it, either entirely free, or in a state of such loose com-
bination that they can be removed by the air-pump. But it cannot
be doubted, that a portion of the effect consists in the oxidation of the
proteine of the fibrinous constituent ; since the fibrin of arterial blood
possesses properties that distinguish it from that of venous. And it
seems probable, also, for the reasons formerly stated, that the hemato-
sine of the red corpuscles undergoes a change under the influence of ^
oxygen in the lungs, and a converse change in the systemic capillaries,
where it is subjected to the influence of carbonic acid. This much
appears tolerably certain : — that a part of the oxygen imbibed in the
lungs, is appropriated to the oxidation of the matters set free by the
decomposition of the solid tissues; — whilst another part enters into
combination with fatty, saccharine, or farinaceous matters, existing in
the blood itself, and destined to be carried oflfin the form of carbonic
acid and water, without ever entering into the composition of the solid
fabric. The relative amounts of carbonic acid formed in these two
modes, vary in different animals, and in diff*erent states of the same
individual ; for a man in a warm atmosphere, taking a moderate
amount of exercise, may thus set free, by the waste of his muscular
and other tissues, a sufficient quantity of carbon, for the maintenance
of his animal heat by its union with oxygen ; but this is far from
being sufficient, when a larger amount of heat must be evolved, to
sustain the temperature of the body in a colder climate.

701. The blood parts in the lungs with a very large amount of
moisture; for the inspired air is always saturated with fluid, as soon
as it reaches the air-cells ; and, as it is heated at the same time to
about 98°, it thus receives a considerable addition, even if it were
previously charged with as much as it could contain at a lower tempe-
rature. The total quantity of fluid thus disengaged will vary, there-
fore, with the amount previously contained in the atmosphere ; being
greater as this was less, and vice versa ; the expired air being always
charged with as much as it can contain at the temperature of 98° or
99°. It cannot be doubted, that a great part of this water is a simple

EXHALATION OF WATER FROM THE LUNGS.— ASPHYXIA. 399

exhalation of that which has been absorbed ; but, on the other hand,
it seems probable that a portion of it may be actually formed in the
system, by the union of a portion of the oxygen absorbed in the lungs,
with the hydrogen of the combustible matters of the blood. In the
various forms of saccharine and farinaceous aliments, the proportions
of hydrogen and oxygen are such as would of themselves form water,
when the carbon is withdrawn ; but in oily and fatty matters, the
proportion of oxygen is far too small thus to neutralize the hydrogen ;
and it seems likely that, by their oxidation in the blood, as by their
combustion elsewhere, water is actually generated by the union of
atmospheric oxygen with their hydrogen, whilst carbonic acid is pro-
duced by its union with their carbon.

702. Along with the water thus extricated from the lungs, a certain
amount of organic matter is set free. If the fluid be collected in a
closed vessel, and be exposed to warmth, a very evident putrid odour
is exhaled from it ; and if the expired air be made to pass through
sulphuric acid, that liquid is coloured red. Every one knows that the
breath itself possesses, occasionally in some persons, and constantly in
others, a fetid taint ; when this does not proceed from carious teeth,
ulcerations in the air-passages or lungs, or other similar causes, it must
result from the excretion of the odorous matter, in combination with
watery vapour, from the pulmonary surface. That this is the true
account of it seems evident, from the analogous phenomenon of the
exhalation of turpentine, camphor, alcohol, and other odorous sub-
stances, which have been introduced into the venous system, either
by natural absorption, or by direct injection ; and also from the sud-
denness with which the odour manifests itself, when the digestive
apparatus is slightly disordered.

5. Effects of Insufficiency^ or Suspension^ of the Aerating Process,

703. The change which the Blood undergoes, by being brought
into relation with atmospheric air in the respiratory organs, is so
important to life, that the entire suspension of it inevitably produces
a fatal termination, at no remote period ; and if it be insufficiently
performed, various disorders in the system are nearly sure to manifest
themselves. The state which is induced by the entire suspension of
the aerating process, is termed Asphyxia ; a word which literally
means the absence of pulse, and would be applicable, therefore, to the
stoppage of the circulation from any cause ; though it is usually em-
ployed to designate the particular condition, resulting from suspended
respiration. Asphyxia may be produced in aquatic animals, as well
as in those which breathe air, by cutting them off from the influence
of the atmosphere ; for if a Fish be placed in water from which the
air has been expelled by boiling, it is precisely in the condition of an
air-breathing animal placed in a vacuum, since it has no power of
obtaining oxygen by decomposing the water it inhabits, and is en-
tirely dependent for the aeration of its blood, upon the air that is

400 ASPHYXIA ;--ITS PHENOMENA.

absorbed by the liquid. Again, if a fish be placed in water impreg-
nated with carbonic acid, its death is nearly as instantaneous as that
of an air-breathing animal immersed in an atmosphere of that gas.

704. Asphyxia may result from a great variety of causes. Thus
there may be a mechanical obstruction to the entrance of air through
the trachea; as in hanging, strangulation, or drowning; or as in
occlusion of the aperture of the glottis, by cedema of its lips, or by the
presence of a foreign body in the larynx. Or, again, the passage may
be perfectly free, and yet no air may enter, in consequence of some
obstacle to the performance of the respiratory movements. This
obstacle may be mechanical ; as when a quantity of earth has fallen
round the body, in such a manner as completely to prevent the disten-
sion of the chest and abdomen. Or it may result (and this is a most
frequent occurrence) from torpidity or complete inactivity of the gan-
glionic centre, which is concerned in the respiratory actions ; or from
interruption to the transmission of its influence along the nervous
trunks. Further, when there is no obstacle to the free ingress or
egress of air. Asphyxia may be produced by the want of oxygen in
the atmosphere that is respired, or by the presence of carbonic acid
in too large an amount. And the presence of other gases, which exert
a directly poisonous influence on the blood, — such as sulphuretted
hydrogen, — produces a state, which may be included under the same
general description.

705. Now when, from any of these causes, the free exchange of
carbonic acid for oxygen in the pulmonary capillaries is checked, the
first effect of the interruption appears to be, the stagnation of the
blood in the pulmonary capillaries. This stagnation is evidently due,
not to any deficiency of power in the heart ; for that organ is not yet
affected ; but to the insufficiency of the heart's power, acting alone,
to drive the blood through the pulmonary capillaries; the force which
should be generated by chemical changes in them (§ 598), being
deficient. The stagnation is not, however, complete at first ; since
the quantity of oxygen contained in the lungs is sufficient to produce
an imperfect arterialization of the blood ; and the blood thus partially
changed is transmitted to the left side of the heart, and is thence pro-
pelled to the system. Owing to its half-venous condition, it cannot
exert its usual stimulating influence on the tissues, especially the
muscular and nervous ; and their powers are consequently weakened.
For the same reason, it does not receive its usual auxiliary force in
the systemic capillaries (§ 599); since the changes, which it ought to
undergo in them, can only be partially performed.

706. As the air included in the lungs loses more and more of its
oxygen, and is more and more charged with carbonic acid, the aera-
tion of the blood in the pulmonary capillaries becomes more and more
imperfect ; the quantity of blood which is allowed to return to the
heart is gradually diminished, and its condition becomes more and
more venous; and at last, the pulmonary circulation is altogether sus-
pended. From the relation which the respiratory circulation bears to

ASPHYXIA ;— ITS PHENOMENA AND TREATMENT. 401

the systemic, in all the higher classes of animals, save Reptiles, it
follows that the systemic circulation must in like manner be brought
to a stand. The venous blood accumulates in the pulmonary artery,
in consequence of the obstruction of its capillaries ; it distends the
right cavities of the heart ; and the accumulation extends to the
venous system of the body in general, especially affecting those or-
gans which naturally receive a large quantity of venous blood, such
as the liver and spleen. The arterial system, on the other hand, is
emptied in a corresponding degree; nearly all its blood having passed
through the systemic capillaries; and no fresh supplies being received
from the heart. From this deficiency, and from the venous character
of the blood which the systemic arteries do contain, it results that the
nervous and muscular systems lose their power; insensibility comes
on, at first accompanied with irregular convulsive movements ; but
in a short time there is a total cessation of all movement except that
of the heart ; and the pulsations of that organ become feebler and
feebler, until they cease altogether. The immediate cause of the
cessation of the heart's action appears to be different on the two
sides. Both are equally affected by the want of arterial blood in the
capillaries of their own substance; but the right side suffers from
over-distension, which produces a sort of paralysis of its muscular-
tissue ; whilst the left side retains its contractility, but is not excited
to contraction, for want of the stimulus of arterial blood in its cavi-
ties.

707. In those warm-blooded animals, which are not endowed with
any special provision for enabling them to sustain life during the pro-
longed suspension of the respiratory process, insensibility and loss of
voluntary power almost invariably supervene within a minute and a
half, after the admission of air to the lungs has been entirely prevent-
ed ; though the respiratory efforts and convulsive actions, which are
dependent upon the medulla oblongata and spinal cord, may continue
for a minute or tw^o longer. The circulation generally comes to a
complete stand within ten minutes at farthest. — The chief exceptions
are in the case of diving animals, which are provided with large
arterial and venous reservoirs, that serve to maintain the circulatioa
during a prolonged suspension of the respiratory process ; for the arte-
rial plexuses being ordinarily filled, they afford a supply of aerated
blood to the systemic capillaries, when other blood is wanting ; and
the reservoirs connected with the venous system, which were pre-
viously empty, receive this blood, and prevent it from exercising;
■undue pressure on the heart. To such an extent is this provision,
carried in some animals, that the Whale has been known to remain
under water for an hour. Another exception exists in the case of
hybernating Mammals, which are reduced for a time to the condition
of cold-blooded animals; and which can, like the latter, sustain a
prolonged suspension of the aerating procees. And there is reason
to believe that, in the state of Syncope or fainting, — in which the
circulation is already reduced to a very low amount, in consequence
26

402 ASPHYXIA ;— ITS PHENOMENA AND TREATMENT.

of a partial failure in the heart's power, all the functions of the body
being nearly suspended, and the demand for aeration being conse-
quently very small, — the respiration may be suspended for a long
period, even in the JHuman subject, without fatal results. Thus more
than one case has been credibly recorded, in which recovery has taken
place after complete submersion for more than three-quarters of an
hour ; and it is probable that, in these instances, a state of Syncope
came on at the moment of immersion, through the influence of mental
emotion, or of concussion of the brain.

708. In the restoration of an animal from the state of Asphyxia, it
is above all things of importance to renew the air in the lungs ; for in
this way the blood in the pulmonary capillaries will be aerated ; the
capillary circulation will be re-established ; the right side of the heart
will be relieved of its excessive load of venous blood ; and the left
side will receive the stimulus of a fresh supply of arterial blood ; so
that, if its movements have not ceased altogether, it may be speedily
restored to due activity. At the same time, the temperature of the
body should be kept up by artificial warmth ; and the circulation in
the skin should be excited by friction. Where no other means are
at hand for introducing pure air into the lungs (of which means the
application of galvanism along the course of the phrenic nerve, so
as to produce contraction of the diaphragm, will probably be the
most effectual), the object may be attained by forcibly compressing
the trunk on all sides, so as to empty the lungs as much as possi-
ble, and then allowing the chest to dilate again, by the elasticity
of its walls. In this manner, a large proportion of the carbonic
acid may be expelled, and a considerable proportion of the fresh air
introduced, in the course of a few, minutes. If air be blown into
the lungs by the bellows, great care must be taken to prevent the
employment of too much force, which is likely to produce rupture of
the air-cells.

709. Now^ when, from the more prolonged action of various causes,
that impede the due performance of the respiratory function, the
aeration of the blood in the lungs is insufficient for health, though not
such as to produce a complete stagnation of the movement, a variety
of results may follow ; of which some, or others, will manifest them-
selves according to the condition of the general system, and the pecu-
liarities of the individual. Thus deficient respiration has an undoubted
tendency to produce, in some persons, what is termed " fatty degene-
ration" of the liver; the fatty matter, which ought to be eliminated
by the respiratory process, being thrown upon the liver to be sepa-
rated by it, and distending its cells (§ 723). And there is reason to
believe, that a similar cause may produce fatty degeneration of the
kidney, in cases where there is a peculiar determination of blood to
that organ. Again, the due elaboration of the fibrin of the blood is
undoubtedly prevented by an habitually deficient respiration ; and
various diseases, which result from the imperfect performance of this
elaboration, consequently manifest themselves. The Scrofulous dia-

1

OF THE SECRETING PROCESS IN GENERAL. 403

thesis is thus frequently connected with an unusually small capacity
of the chest. — Further, an habitual deficiency of respiration may im-
pede, though it does not check, the circulation in the lungs ; and thus
a tendency arises, in various pulmonary diseases, to an overloading of
the pulmonary arteries, to a dilatation of the right cavities of the
heart, and to a congestion of the venous system in general, as marked
by lividity of the surface, by venous pulsation, &c. This state may
result, not merely from obstruction in the lungs themselves, but from
deficiency of the respiratory movements, consequent upon torpidity of
the medulla oblongata (as in apoplexy and narcotic poisoning), or
upon partial interruption of the nervous circle requisite for all reflex
movements. Thus when the par vagum is divided, the number of
respiratory movements is greatly diminished, and a partial stagnation
of the blood in the lungs is the result. The same happens in certain
forms of typhoid fever, in which the respiratory movements are pre-
ternaturally slow, in consequence of torpidity of the medulla oblon-
gata. Now in this state, an effusion of the watery part of the blood
into the air-cells of the lungs (as in other cases of obstructed circula-
tion) is very liable to occur ; and w^hen the lungs are thus loaded
with fluid, the respiratory process is still more impeded, and the dis-
order has thus a tendency to increase itself.

CHAPTER IX.

OF SECRETION.

1. Of the Secreting process in general; and of the Instruments by
which it is effected,

710. We have seen that, in the process of Nutrition, the circulat-
ing current not only deposits the materials, which are required for the
renovation of the solid tissues ; but also takes back the substances,
which are produced by the decay of these, and which are destined to
be thrown off from the body. We have also seen that it supplies the
materials of certain fluids, which are separated from it to effect various
purposes in the economy ; — such as the Salivary and Gastric fluids,
which have for their office to assist in the reduction of the food. Now
the process, by which the fluids of the latter kind are separated from
the Blood, is precisely the same in character as that, by which the
products of decay are eliminated from it ; and the structure of the or-
gans concerned in the two is essentially the same. Hence both pro-
cesses are commonly included under the general term Secretion, which
simply denotes separation. Considered in its most general point of
view, this designation may be applied to every act, by which sub-

404 NATURE OF THE SECRETING PROCESS.

stances of any kind are separated from the blood. Thus the function
of the floating cells, which are concerned in the production of Fibrin
(§ 213), may be termed one of secretion; because they draw from
the blood a supply of Albumen, upon which their converting action
is exercised ; but as the product of their operation is returned to the
blood again, and is employed for higher purposes in the economy,
the process is usually termed Assimilation. In the same manner, the
elaborating action of the Lymphatic Glands, with the Spleen, Thy-
mus Gland, &c., is not usually termed Secretion; since, although it
is exercised upon matter drawn from the blood, the product appears
to be delivered back into the circulating current, through the medium
of the Lymphatic System (Chap. V). With much more justice, how-
ever, the process of Respiration may be regarded as one of Secretion ;
for it consists, as we have seen, in the constant elimination of a sub-
stance from the blood, which cannot be retained in it without the
most injurious consequences.

711. There is an important difference in the characters of the prin-
cipal products of the Secreting process ; which is connected with the
purposes that are to be answered by their separation. Some of these
products are altogether different from the ordinary constituents of the
animal fabric, and from the materials which the blood supplies for the
nutrition of these. So different are they, that their presence in the
circulating current has an injurious effect; and the great object of
their separation is the maintenance of the purity of the blood. These
poisons, for such they may be considered, are generated in the system
by the decay and decomposition to which its several parts are liable ;
and they are just as noxious to it, as if they were absorbed from without.
We have seen that the retention of Carbonic acid in the blood for
even a few minutes is fatal ; both by putting a stop to the circulation,
and by acting unfavourably upon the substance of some of the most
important organs in the body. The same fatal result attends the
retention of Urea and of Biliary matter, which are among the other
products of the decomposition of the tissues ; but, although as certain,
it is not so speedy, because the general circulation is not affected by
the loss of secreting power on the part of the Kidneys and the Liver,
and because the accumulation of the noxious matter is slower. — On
the other hand, the ingredients that are met with in those secreted
fluids, which are destined to answer some purpose in the economy,
almost invariably bear a close correspondence with the ordinary ma-
terials of the blood. Thus in the Salivary, Gastric, Pancreatic, and
Lachrymal fluids, the principal part of the solid matter consists of the
saline and of the albuminous constituents of the blood, — the latter in
a more or less altered condition. In Milk, again, we trace the ordi-
nary constituents of the blood, with very little change. Thus it
appears, that the separation of these fluids is not required so much to
maintain the Blood in a state of purity, as to supply what is needed
for some subsequent operation in the economy ; and hence, if the
secreting process be interrupted, in the case of any one of them, the

NATURE OF THE SECRETING PROCESS. 405

suspension has usually no further effect, than that of disturbing the
process to which the fluid is usually subservient. If the secretion of
Gastric fluid be checked, for example, under the influence of strong
mental emotion, the Digestive operation is prevented from taking
place.

712. The essential character of the true Secreting operation seems
to consist, — not in the nature of the action itself, for this is identical
with those of Assimilation and Nutrition, being (as we have seen,
§ 239), a process of cell-growth, — but in the position in which the
cells are developed, and the mode in which the products of their
action are afterwards disposed of. Thus the cells at the extremities
of the intestinal Villi (§ 241), the cells of which the Adipose tissue
is made up (§ 259), and the cells of which the greater part of the
substance of the Liver is formed (§ 239), all have an attraction for
fatty matter ; and draw it from the neighbouring fluids, at the expense
of which they are developed, to store it up in their own cavities.
But the cells of the first kind, when they have come to maturity, set
free their contents, which are delivered to the absorbent vessels, to
be introduced into the circulating current : — those of the second kind
seem more permanent in their character, and retain their contents, so
as to form part of the ordinary tissues of the body, until they are re-
quired to give them up for other purposes, when the matters, which
they have temporarily separated from the circulating current, are
restored to it again without change ; — and the cells of the third class,
when they liberate their contents (which they are continually doing),
cast them forth into the hepatic ducts, by which they are carried into
the intestinal canal, whence a portion of them at least is directly con-
veyed out of the body.

713. It is, then, in the position of the Secreting cells, — which causes
the product of their action to be delivered upon a Jree surface, com
municating, more or less directly, with an external outlet, — that their
distinctive character depends. All the proper Secretions ' zve thus
either poured out upon the exterior of the body, or into cavities pro-
vided with orifices that lead to it. Thus we shall see that a con-
siderable quantity of solid matter, and a very large quantity of fluid,
of which it is desirable that the system should be freed, are carried
off from the Cutaneous surface. Another most important secretion,
containing a large quantity of solid matter, and serving also to regu-
late the quantity of fluid in the body, — namely, the Urinary, — is set
free by a channel expressly adapted to convey it directly out of the
body. The same may be said of the Mammary secretion ; which is
separated from the blood, not to preserve its purity, nor to answer
any purpose in the economy of the individual, but to afford nutriment
to another being. And of the matters secreted by the very numerous
glandulse situated in the walls of the intestinal canal, a great part are
obviously poured into it for no other purpose, than that they may be
carried out of the body by the readiest channel.

714. The cells covering the simple membranes that form the free
surfaces of the body, whether external or internal, are all entitled to

406 CHARACTER OF GLANDULAR STRUCTURE.

be regarded as secreting cells ; since they separate from the blood
various products which are not again to be returned to it. But the
secreting action of some of these seems to have for its object the
protection of the surface ; thus the epidermic cells secrete a horny
matter, by which density and firmness are imparted to the cuticle ;
whilst by the epithelial cells of the Mucous Membrane of the alimen-
tary canal, and of other parts, their protective Mucus seems to be
elaborated. But in general we find that special organs, termed Glands,
are set apart for the production of the chief secretions ; and we have
now to consider the essential structure of these organs, and the mode
of their operation. — A true Gland may be said to consist of a closely
packed collection of follicles, all of which open into a common chan-
nel, by which the product of the glandular action is collected and
delivered. The follicles contain the secreting cells in their cavities ;
whilst their exterior is in contact with a network of blood-vessels,
from which the cells draw the materials of their growth and deve-
lopment (Fig. 90). In any one of the higher animals, we may trace
out a series of progressive stages of complexity, in the various glands
included within their fabric ; and in following any one of the glands,
that attain the highest degree of development (such as the Liver or
Kidney), through the ascending scale of the Animal series, we should
trace a very similar gradation from the simplest to the most complex
form.

715. That there is nothing in the form or disposition of the com-
ponents of the glandular structure, which can have any influence
upon the character of the secretion it elaborates, is evident from the
fact, that the very same product, — e. g., the Bile, or the Urine, — is
found to issue from nearly every variety of secreting structure, as we
trace it through the different groups of the Animal kingdom. The
peculiar power, by which one organ separates from the blood the
elements of the Bile, and another the elements of the Urine, whilst a
third merely seems to draw off a certain amount of its albuminous
and saline constituents, is obviously the attribute of the ultimate
secreting cells, which are the real agents in the secreting process
(§ 239). Why one set of cells should secrete bile, another urea,
and so on, we do not know ; but we are equally ignorant of the
reason for which one set of cells converts itself into Bone, another
into Muscle, and so on. This variety in the endowments of the cells,
by whose aggregation and conversion the fabric of the higher Ani-
mals is made up, is a fact which we cannot explain, and which must
be regarded (for the present, at least), as one of the " ultimate facts"
of Physiological Science.

716. Passing by the extended membranous surfaces, and the pro-
tective cells with which they are covered, we find that the simplest
form of a secreting organ is composed of an inversion of that suriface,
into a series of follicles, which discharge their contents upon it by
separate orifices. Of this we have an example in the ^a^/ric follicles,
even in the higher animals ; the apparatus for the secretion of the
Gastric fluid never attaining any higher condition than that of a

SIMPLEST FORMS OF GLANDULAR STRUCTURE.

407

series of distinct follicles, lodged in the walls of the stomach, and
pouring their products into its cavity by separate apertures. In Fig.

Fig. 103.

Fig. 104.

Glandular follicles in ventriculus
succenturiatus of Falcon.

Origin of the Liver from the intestinal wall, in the
embryo of the Fowl, on the fourth day of incubation :
— a, heart ; b, intestine ; c, everted portion giving ori-
gin to liver ; d, liver ; e, portion of yolk-bag.

Fig. 105.

103 is represented a portion of the Ventriculus succenturiatus of a
Falcon ; in which the simplest form of such follicles is seen. A some-
what more complex condition is seen in some of the Gastric follicles
of the Human stomach (Fig. 75) ; the
surface of each follicle being further
extended by a sort of doubling upon
itself, so as to form the commencement
of secondary follicles, which open out
of the cavity of the primary one. —
Now a condition of this kind is common
to all glands, in the first stage of their
evolution ; and in this stage we meet
with them, either by examining them
in the lowest animals in which they
present themselves, or by looking to an
early period of their embryonic deve-
lopment in the highest. Thus, for ex-
ample, the Liver consists, in certain
Polypes and in the lowest MoUusca, of
a series of isolated follicles, lodged in
the walls of the stomach, and pouring
their product into its cavity by separate orifices ; these follicles being
recognized as constituting a biliary apparatus, by the colour of their
secretion. And in the Chick, at

an early period of incubation, the ^ig. loe.

condition of the Liver is essen-
tially the same with the preced-
ing ; for it consists of a cluster
of isolated follicles, not lodged
in the walls of the intestine, but
clustered round a sort of bud or
diverticulum ofthe intestinal tube,
which is the first condition of the

Rudimentary Pancreas from Cod ;— a,
pyloric extremity of stomach ; b, intes-
tine.

Mammary Gland of Ornithorhyucus.

408 DIFFERENT FORMS OF GLANDULAR STRUCTURE.

hepatic duct, and into which they discharge themselves (Fig. 104).
So, again, the Pancreas first presents itself in the condition of a group
of prolonged follicles, or cceca, clustered round the commencement of
the intestinal tube (Fig. 105); which is its permanent condition in
many Fishes. And the Mammary Gland possesses an equally simple
structure in the lowest of all the Mammalia (to which group it is re-
stricted ; — namely, in the Ornithorhyncus (Fig. 106).

717. The next grade of complexity is seen, where a cluster of the
ultimate follicles open into one common duct, which discharges their
product by a single outlet ; a single gland often containing a number
of such clusters, and having, therefore, several excretory ducts. A
good example of such a condition, in which the clusters remains iso-
lated from one another, is seen in the Meibomian glands of the eye-
lid (Fig. 107); each of which consists of a double row of follicles, set
upon a long straight duct, that receives the products of their secreting
action, and pours them out upon the edge of the eyelid. And of the
more complex form, in which a number of such clusters are bound
together in one glandular mass, we have an illustration in the acces-
sory glands of the genital apparatus, in several animals, which dis-
charge their secretion into the urethra by numerous outlets (Fig.
108); or in the Mammary glands of Mammalia in general, the ulti-
mate follicles of which are clustered upon ducts that coalesce to a

Fig. 107. Fig. 108. Fig. 109.

Meibomian glands of upper Portion of Cowper's gland, Lobule of Lachrymal Gland ;

lid of new-born infant. from Hedgehog; the follicles from foetal sheep,

distended with air.

considerable extent, though continuing to form several distinct trunks
even to their termination. Such glands may be subdivided, there-
fore, into glanduU or lobules, that remain entirely distinct from each
other (Fig. 109).— In the highest form of Gland, however, all the
ducts unite; so as to form a single canal, which conveys away the
products of the secreting action of the entire mass. This is the con-
dition in which we find the Liver to exist, in most of the higher ani-
mals; also the Pancreas, the Parotid Gland, and many others. In
•some of these cases, we may still separate the gland into numerous
distinct lobules, which are clustered upon the excretory duct and its
branches, like grapes upon a stalk ; in others, however, the branches

DEVELOPMENT OF GLANDS. 409

of the excretory duct do not confine themselves to ramifying, but
inosculate so as to form a network, which passes through the whole
substance of the gland, and which connects together its different
parts, so as to render the division into lobules less distinct. This
seems to be the case in regard to the Liver of the higher Vertebrata.
718. Whatever degree of complexity, however, prevails in the
general arrangement of the elements of the Glands in higher animals,
these elements are themselves everywhere the same, consisting of
follicles that enclose the real secreting cells (Figs. 110 and 111).
Now from the history of the development of Glands in general, it ap-
pears that the follicles may be considered dis parent cells; and that the

Fig. 110. Fig. 111.

Two follicles from the liver of Careinus Ultimate follicles of Mammary gland,

nuEnos (Common Crab), "with their contain- with their secreting cells, a, a; — b, b, the

ed secreting cells. nuclei.

secreting cells in their interior constitute a second generation, developed
from the nuclei or germinal spots on the walls of the first. It has been
pointed out by Mr. Goodsir, that the continued development and de-
cay of the glandular structure, — in other words, the elaboration of its
secretion, may take place in tw^o different modes. In one class of
Glands, the parent-cell, having begun to develop new cells in its in-
terior, gives way at one point, and bursts into the excretory duct, so
as to become an open follicle, instead of a closed cell : its contained
or secondary cells, in the progress of their own growth, draw into
themselves the matter to be eliminated from the blood, and, having
attained their full term of life, burst or liquefy, so as to discharge
their contents into the cavity of the follicle, whence they pass by its
open orifice into the excretory duct: and a continual new production
of secondary cells takes place from the germinal spot or nucleus, at
the extremity of the follicle, which is here a permanent structure. In
this form of gland, we may frequently observe the secreting cells ex-
isting in various stages of development within a single follicle ; their
size increasing, and the character of their contents becoming more
distinct, in proportion to their distance from the germinal spot (which
is at the blind termination of the follicle), and their consequent proxi-
mity to the outlet (Fig. 110). In some varieties of such glands, how-
ever,— as in the greatly prolonged follicles, or tubuli uriniferi, of the
kidney, — the production of new cells does not take place from a single
germinal spot at the extremity of the follicle, but from a number of
points scattered through its entire length.

719. In the second type of Glandular structures, the parent-cell

410

COMPARATIVE STRUCTURE OF THE LIVER.

does not remain as a permanent follicle ; but, having come to maturity
and formed a connection with the excretory duct, it discharges its
entire contents into the latter, it then shrivels up and disappears, to be
replaced by newly-developed follicles. In each parent-cell of a gland
formed upon this type, we shall find all its secondary or secreting cells
at nearly the same grade of development ; but the different parent-
cells, of which the parenchyma of the gland is composed, are in very
diff*erent stages of growth, at any one period, — some having discharged
their contents and being in progress of disappearance, whilst others
are just arriving at maturity and connecting themselves with the
excretory duct; others exhibiting 'an earlier degree of development of
the secondary cells; others presenting the latter in their incipient con-
dition; whilst others are themselves just starting into existence, and
as yet exhibit no traces of a second generation. — The former seems to
be the usual type of the ordinary Glands ; the latter is chiefly, if not
entirely, to be met with in the Spermatic glands.

2. Of the Liver,

720. The Liver is more rarely absent than any other Gland ; being
discoverable, under some form or other, in all but the very lowest
members of the Animal kingdom. Its simple condition in the higher
Polypes has been already noticed (§ 716) ; and it is met with, under
an almost equally simple form, in the Star-fish. As we ascend the
scale, however, w^e find it assuming a much greater importance, and
presenting a great increase in size. This is particularly the case in
the Molluscous classes ; and also in the Crustacea, — a class which, in
mode of respiration and in general habits, bears a great resemblance to
the MoUusca. In nearly all such animals, the Liver makes up a large
proportion of the mass of the body. It usually consists of a series of
large follicles, which branch out into smaller ones (Figs. 112 and 113),

Fig. 112.

Fig. 113.

Lobule of Liver of Squilla Mantis; exterior.

Lobule of Liver of Squilla Mantis cut open.

and of which several open into one excretory duct; but these ducts
remain separate, and discharge their contents into the intestine by
several distinct orifices. — In Insects and other air-breathing Articu-

STRUCTURE OF THE LIVER.

411

Fig. 114.

lata, however, the Liver is much less developed ; and its type remains
much simpler. We usually find it consisting of a small number of
csecal tubuli, which open separately into the intestinal canal, just
below the stomach. These tubuli are often so long, as to pass several
times from one extremity of the visceral cavity to the other, being
doubled upon themselves ; in other instances, we find that the prin-
cipal tube or canal is beset with rows of short follicles, somewhat in
the manner of Fig. 107. But they never cluster together, so as to
form a solid glandular mass. The low development of the liver, in
these animals, bears an evident relation with the high development
of their respiratory apparatus ; whilst, the respiration being compara-
tively feeble in the aquatic Mollusca and Crustacea, the development
of the liver in those classes is enormous.

721. There is much difficulty in ascertaining the mode in which
the elementary constituents of the Liver are arranged, in the fully-
developed condition of that organ in the higher Vertebrata. At an
early period of its development,
as already remarked, it may be
easily shown to consist, in the
Fowl, of a series of distinct caeca,
clustered round a projection from
the intestinal canal, and opening
separately into it (Fig. 104) ; and
it is a peculiarly interesting fact,
that this very condition should
exist as the permanent form of the
Liver, in that curious little fish,
the Amphioxus or Lancelot, which
retains the embryonic type in so
many parts of its conformation.
In the Tadpole, again, the distinct
cseca are very evident (Fig. 114);
but here we see that the projection
of the intestinal canal, instead of
being a simple wide csecum, has

become extended in length and contracted in diameter, at the same
time dividing and subdividing, so as to form an arborescent excretory
duct, whose ramifications extend through the entire glandular mass.
In this manner, then, is formed the complex system of hepatic ducts,
which we find in the liver of the higher Vertebrata, branching out
from the main trunk. But the mode in which the ultimate ramifica-
tions of these are arranged, and their relations with the secreting cells,
which make up the parenchyma of the gland, have not yet been fully
elucidated. The following are the principal facts, that have been
ascertained on the subject.

722. The entire Liver is made up of a vast number of minute
lobules, of irregular form, but about the average size of a millet-seed.
Each of these lobules contains the component elements, of which the

Liver of Tadpole ; showing distinct and free
caecal terminations of the biliary ducts.

412

DISTRIBUTION OF BLOOD-VESSELS OF THE LIVER.

entire organ is made up ; — namely, branches of the hepatic artery and
vein, branches of the portal vein, branches of the hepatic ducts, and
secreting cells. The lobules are connected together in part by areolar
tissue, but in great part by the anastomosis of the blood-vessels and
hepatic ducts, which supply the adjoining lobules; indeed there is
frequently no definite division of the glandular substance into lobules,
other than that, which is marked out by the arrangement of these
canals (Figs. 115 and 117). The branches of the Hepatic Artery are
principally distributed upon the walls of the hepatic ducts, and upon
the trunks and branches of the portal and hepatic veins, supplying
them with their vasa vasorum; also upon Glisson's capsule and its
prolongations into the substance of the liver, — which prolonga-
tions form the greatest part of the connecting structure, that holds
together the several elements. There is strong reason to believe,
that the blood which the liver receives from the hepatic artery is not
destined to supply the materials for the biliary secretion, until it has
become venous by traveling through the network, in which it is sub-
servient to the nutrition of the tissues it permeates, as it is in other
parts of the systemic capillary system. — The supply of blood, from
which the materials of the biliary secretion are chiefly drawn, is
afforded by the Vena PortcB, which collects it as a Vein from the chy-
lopoietic viscera, and which then subdivides as an Artery to distribute
it to the different parts of the Liver. Its branches proceed to the cap-
sules of the lobules, covering the whole external surface of the latter
with their ramifications, and sending capillary twigs inwards, which
converge towards the centre of each lobule (Fig. 115). As the prin-

Fig. 116.

Horizontal section of three superficial lobules,
showing the two principal systems of blood-ves-
sels ; 1, 1, mtra-lobular veins, proceeding from the
Hepatic veins ; 2, 2, inter-lobular plexus, formed
by branches of the Portal veins.

Connection of the lobules of the Liver
with the Hepatic vein; 1, trunk of the vein;
2, 2, lobules depending from its branches,
like leaves on a tree ; the centre of each
being occupied by a venous twig— the In-
tralobular Vein.

cipal branches of these veins ramify in the spaces between the lobules,
they are termed in^er-lobular veins.— On the other hand, the branches

HEPATIC DUCTS, AND CELLS OF PARENCHYMA.

413

of the Hepatic Vein pass from the trunks to the centre of each lobule,
from which they send out diverging capillary twigs towards the cir-
cumference ; and these last, coming into connection with the converg-
ing capillaries of the portal vein, establish a free capillary communi-
cation between the interior and exterior of each lobule. Thus the
portal blood is first distributed to its exterior, then penetrates its sub-
stance, and then, after permeating the parenchymatous substance in
numerous minutely-divided streams, is collected and carried off by the
hepatic vein, of which a twig originates in the centre of each lobule.
Owing to the peculiar position of the branches of the hepatic vein in
the centre of each lobule, the lobules are appended to its mai^ trunks
almost in the manner of leaves upon a stem (Fig. 116). — Thje precise
relation of the capillaries of the hepatic artery with those of the por-
tal and venous systems, has not yet been well ascertained ; but there
seems reason to believe, with Mr. Kiernan, that the arterial capillaries
discharge themselves into the ultimate ramifications of the portal vein ;
and that thus the blood of the former, having become venous by
transmission through the nutritive capillaries of the liver, mingles
with the other venous blood collected by the vense portse, to supply
the materials of the secretory function, which are eliminated from it
during its passage into the hepatic vein.

723. The Hepatic Ducts also form a plexus, which surrounds the
lobules ; connecting them together, and sending branches towards the
interior of each. The mode in which they terminate, however, and
the precise relation in which they stand to the hepatic cells, which
form nearly the entire parenchyma of the Gland, are yet unexplained.

Fig. 118.

Horizontal section of two superficial lobules, showing
the interlobular plexus of biliary ducts ; 1, 1, intralobu-
lar veins; 2, 2, trunks of biliary ducts, proceeding from
the plexus which traverses the lobules ; 3, interlobular
tissue ; 4, parenchyma of the lobules. (After Kiernan.)

Glandular cells of Liver:— a, nucleus'
, nucleolus ; c, adipose particles.

These cells are of a flattened spheroidal form, and commonly lie in
piles, their faces adhering to one another ; and these piles seem to be
directed especially from the circumference to the centre of each lobule.
Every one of them presents a distinct nucleus; and the cavity of the
cell is filled with yellow amorphous biliary matter, having one or two
large adipose globules, or five or six small ones, intermingled with it.

414 CHEMICAL COMPOSITION OF BILE.

Their diameter is usually from l-1500th to l-2000th of an inch ; and
they are easily obtained in a separate condition, by scraping a piece
of fresh Liver. The biliary matter which they contain, marks them
out as the real agents in the secreting process ; this process consisting,
it is evident, in the growth of the hepatic cells, w^hich, in the course
of their development, eliminate from the blood the biliary matter, for
"which they have a special affinity. The mode in which the particles
thus eliminated, are discharged into the hepatic ducts, to be by them
conveyed to the intestine, cannot be understood, until the relation
between the secreting cells and the ultimate ramifications of the ducts
shall have been more precisely determined.

724. The Bile which has been secreted by the hepatic cells, and
which has found its way into the ramifications of the hepatic ducts,
may be directly conveyed by the trunk of the latter into the intestine,
or it may regurgitate along the cystic duct into the gall-bladder. It
is probable that the secreting process is constantly going on ; although,
as in other cases, it may vary in its degree of activity at different times.
"When the process of digestion is taking place, and the small intestine
is filled with chyme, there is probably an uninterrupted flow of bile into
its cavity ; but when the intestine is empty, the bile seems not to be
admitted into it, but rather to flow back into the gall-bladder, in which
it is stored up as in a reservoir, until the time when it may be needed.
In this reservoir it undergoes a certain degree of concentration, by the
absorption of its watery part ; and it also becomes mixed with a large
proportion of mucus, which is secreted by the walls of the gall-bladder.
— As the analyses of Bile have been chiefly made upon the fluid ob-
tained from this receptacle, they probably over-estimate the proportion
of solid matter contained in this secretion ; which is usually stated at
from 8 to 9^^ per cent. Of this solid matter about a tenth consists of
alkaline and earthy salts, corresponding with those of the blood ; whilst
the remainder is made up of organic constituents. These are very
readily decomposed, and enter into new combinations with the sub-
stances employed to separate them ; so that different chemists, by em-
ploying different means of analysis, have obtained results which seem
far from conformable. All are agreed, however, that the chief part
of the solid ingredients of bile are allied \ofat in composition ; con-
sisting of a very large proportion of carbon and hydrogen, and of a
comparatively small amount of oxygen and azote. According to Dr.
Kemp, the organic portion of ox-bile may be represented by the for-
mula 48 Carbon, 42 Hydrogen, 13 Oxygen, and 1 Nitrogen. This
substance, essentially corresponding with the bilic acid, choleic acid,
bilin, picromel, &c., of different Chemists, seems to be a fatty acid,
(§ 261), united with soda, so as to constitute a soap. In healthy bile,
the proportion of Cholesterine appears to be very small ; and it is held
in solution by the preceding ingredient: but in many disordered states,
and especially in disease of the Gall-bladder, this element is present
in much larger amount ; and it usually forms the principal, if not
the sole, ingredient in biliary concretions. It is a white crystalizable

\

PURPOSES OF THE BILIARY SECRETION. 415

fatty matter, somewhat resembling spermaceti, free from taste and
odour, and composed almost entirely of carbon and hydrogen, — its
formula being 36 Carbon, 32 Hydrogen, and 1 Oxygen. — The Colour-
ing matter of Bile is a substance distinct from the preceding; that of
the Ox and other graminivorous animals appears to be identical, or
nearly so, with the Chlorophyll of the leaves on which they feed ; but
that of human bile seems to possess different properties, and to be
derived from the proper constituents of the blood.

725. Regarding the destination and purposes of this secretion in the
Animal economy, the following may be considered as a tolerably com-
plete summary ; though it is difficult to speak with precision on some
points ; since the organic constituents of the Bile are liable to be so
easily altered by various reagents, that they are with difficulty recog-
nized. A portion of the Bile unquestionably passes off, in Man and
most other animals, with the feces. This portion, which includes the
colouring matter, is probably that which would be most injurious, if
retained in the blood, and is most purely excrementitious. But the
soapy portion has quite another destination. Just as ox-gall is com-
monly used to remove grease spots, by its solvent power for fatty mat-
ter, so does the bile seem to act in the living body, by rendering soluble
the fatty matters of the food, and thus enabling them to be absorbed by
the lacteals (§ 494). Hence, if the passage of bile into the intestine be
prevented (as in the recent experiments of Schwann) without any
check to its separation from the blood, the animals gradually lose their
plumpness, and at last die in a state of emaciation, — the fatty matter
of their food not being introduced into their absorbent system, nor ap-
plied to the maintenance of their respiration. The fatty matter of the
bile, when re-absorbed with that of the newly-ingested food, is proba-
bly, like it, carried off by the respiratory process : but it is easily shown,
that the biliary matter cannot supply more than one-sixth or one-
eighth of the amount of carbon eliminated from the lungs in the form
of carbonic acid ; and that it cannot be (as supposed by Liebig) the
chief fuel of the process of combustion, which is kept up through the
agency of those organs.

726. The elements of the Bile may be altogether supplied by the
disintegration of the tissues; and this must certainly be the case, when
the amount of food taken is no more than enough to supply the waste
of the system. We may regard it, then, as one office of the Liver to
remove from the blood such products of that disintegration, as are rich
in carbon and hydrogen. But there can be little doubt, that the Liver
has also for its office, to draw off from the blood any superfluity which
may exist in the non-azotized compounds derived from the food, be-
yond the amount that is requisite for the supply of the respiratory pro-
cess, or that can be deposited as fat. For we continually witness the
results of habitual excess in the amount of such sbstances, in pro-
ducing that state of the system commonly termed bilious; of which all
the symptoms are referable to the accumulation of the elements of the
bile from the blood, and the consequent deterioration in the purity of

416 COMPARATIVE STRUCTURE OP KIDNEY.

the circulating fluid. Where a tendency to such a state exists, proper
means should be taken to stimulate the liver to increased activity ; but
the chief reliance should be placed on the avoidance of those articles of
diet, which contain a large proportion of non-azotized matter, and on
abstinence from superfluous nutriment of any description. That the
less hydro-carbon separated from the blood by Respiration, the more is
eliminated from it by the Biliary secretion, seems to be a general prin-
ciple throughout the Animal kingdom ; the Liver and Respiratory
organs bearing, almost everywhere, an inverse ratio to each other in
their degree of. development.

3. Of the Kidneys and the Urinary Excretion,

727. The Kidneys are perhaps the most purely excreting organs in
the body; their function being to separate from the Blood certain
matters that would be injurious to it if retained ; and these matters
being destined to immediate and complete re-
Fig^ii9. moval from the system. We have seen that,

in the Lungs, the excretion of Carbonic acid
is made subservient to the absorption of Oxy-
gen ; and the separation of a fatty acid from
the blood, which is effected by the Liver, is a
means of introducing a new supply of fatty
matter into the system. There is no ulterior
purpose of this kind in the secreting action of
the Kidney; the product of which is invari-
ably conveyed directly to an outlet, by which
it may be discharged from the body. Some
traces of Urinary organs may be detected in

Embryo of Green Lizard:- ^^^^ ^^ ^hc higher luVCrtebrata ; but it is in
a, heart; 6, duplex aorta; c, FishcS, that they first prCSCUt a Considerable de-
vena cava; d, intestine; e, , ' , % . ^ ,. ,, i Ji it

liver;/, rudiment of Wolffian vclopmeut ; ancl lu ascendmg through the Ver-
Siiifs/' '"'^''"'"'' °' '''" tebrated series, we find them rapidly increasing
in the complexity of their organization, and in
their functional importance, although their size and extent are not so
great. In Fishes the Kidneys very commonly extend the whole
length of the abdomen ; and they consist of tufts of uniform sized
tubules, which shoot out transversely at intervals from the long ure-
ter, and which are connected together by a loose w^eb of areolar tis-
sue, that supports the network of vessels distributed upon their walls.
This condition of the urinary organs is very analogous to that of the
Corpus Wolffianum or temporary kidney of the embryo of higher ani-
mals (Fig. 119,y*). A similar condition is found in the true Kidney
of higher animals at an early grade of development (as shown in Fig.
120) ; the tubuli uriniferi being short and straight. In their more ad-
vanced condition, however, they become long and convoluted ; and
the ramifications of the capillary vessels come into very close relation
with them (Fig. 121). It is in the higher Reptiles, that we first meet

STRUCTURE OF HUMAN KIDNEY.

417

with the distinction between the cortical and medullary substance ;
the former being the part in which the blood-vessels are most copi-

ng. 120,

Kidney of foetal Boa :— the urinary tubes as yet short and straight.

ously distributed, and in which the tubuli have the most convoluted
arrangement ; and the latter consisting chiefly of straight tubuli, con-
verging towards the points at which they discharge themselves into
the ureter (Fig. 122). The bundles of tubuli and their vascular

Fig. 121.

Fig. 122.

Portion of Kidney from Coluber :— a, a, vascular trunk ;
b, 6, ureter; c, c, converging fasciculi of tubuli uriniferi.

Pyramidal fasciculi of tubuli
uriniferi of Bird, terminating in
one of the branches of the ureter.

plexuses remain distinct, however, in Birds and in the lower Mam-
malia, so as to give to the gland a lobulated character; but in the
Human Kidney, they come into closer contact; and the vascular con-
nection between the plexuses of the different bundles is such, as to
prevent any separation into distinct lobules.

728. The act of secretion appears to be effected, as in other Glands,
by the epithelial cells lining the tubuli uriniferi ; these cells drawing
the materials of their development from the vascular plexus upon the
exterior of these tubuli ; and delivering them up, when they have com-
pleted their own term of existence, to be carried off through the open
orifices of the tubuli. But the Kidney contains another apparatus, of
a very peculiar description ; which appears specially destined for the
separation of the superfluous^wic? of the system. When a section of
the Kidney is slightly magnified (Fig. 124, b), the cut surface is seen
to be studded by a number of little dark points ; each one of which,
when examined under a higher magnifying power, is found to consist
of a knot of minute blood-vessels, formed by the convolutions of
thin-walled capillaries (Fig. 125, m). According to the recent inqui-
ries of Mr. Bowman, each one of these knots is included in the
extremity of one of tubuli uriniferi, which swells into a flask-like
capsular dilatation to receive it. Each of these vascular tufts (called
27

418

CIRCULATION IN THE KIDNEY.

Malpighian bodies, after their discoverer), is directly supplied by a
branch of the renal artery (Fig. 125, af) ; which, upon piercing the

Fig. 123.

Fig. 125.

Portion of the Kidney
of a new-born infant, a,
natural size ; 1, 1. Cor-
pora Malpighiana, as
dispersed points in the
cortical substance ; 2,
papilla. B, a smaller
part magnified ; 1, 1, Cor-
pora Malpighiana ; 2, 2,
tubuli urinifcri.

Distribution of the Renal ves-
sels ; from Kidney of Horse :— a,
branch of Renal artery ; a/,
afferent vessel ; m, m, Malpigh-
ian tufts ; €/, e/, efferent vessels;
j7, vascular plexus surrounding
the tubes ; s/, straight tube ; ci,
convoluted tube. Magnified
about 30 diameters.

A section of the Kidney, sur-
mounted by the supra-renal cap-
sule; the swellings upon the surface
mark the original constitution of
the organ, as made up of distinct
lobes. 1. The supra-renal capsule.
2. The vascular portion of the kid-
ney. 3, 3. Its tubular portion, con-
sisting of cones. 4, 4. Two of the
papilla3 projecting into their cor-
responding calices. 5, 5, 5. The
ihree infundibula; the middle 5 is
situated in the mouth of a calyx. 6.
The pelvis. 7. The ureter.

capsule, subdivides into a group of capillaries ; and these, after form-
ing the convoluted tuft, coalesce into a single efferent trunk (e/*),
which may be considered as representing (in a small way) the vena
portse. For the efferent trunks of the Malpighian bodies discharge
their blood into the capillary plexus, which surrounds the tubuli
uriniferi, and from which the solid matter of the urinary secretion is
elaborated ; just as the vena portse supplies the capillary plexus, from
which the biliary secretion is elaborated in the liver. The special
purpose of the Malpighian bodies appears to be, to allow of the trans-
udation of the water of the blood, which is filtered off (so to speak)
through the thin walls of their capillaries, and thus passes into the
tubuli uriniferi. It is well known that the fluid and solid constituents
of the urinary secretion bear no constant relation to each other ; the
amount of fluid depending mainly upon the degree of fullness of the
blood-vessels ; whilst the amount of solid matter is governed, as we
shall presently see, by the previous waste of the tissues. The quan-
tity of fluid in the blood-vessels is governed by the relative amount
that has been absorbed, and that which has been exhaled from the
skin ; so that the quantity to be drawn off by the Kidneys is increased,
either by augmented absorption, or by diminished exhalation. The

CHARACTERS OF THE URINARY EXCRETION. 419

Malpighian bodies seem to act the part of a system of regulating
valves ; permitting the transudation of only enough fluid to dissolve
the solid matter, when there is no superfluity of water in the vessels ;
but allowing the escape of an almost unlimited amount of it, when
increased imbibition has rendered the vessels unusually turgid.

729. The average amount of Urine excreted in twenty-four hours,
by adults who do not drink more than the wants of nature require, is
probably from 30 to 40 oz. ; and its average specific gravity may be
about 1020. The quantity of fluid is usually less, and the specific
gravity of the secretion consequently greater in summer than in win-
ter ; on account of the larger proportion of fluid exhaled by the skin
during the former season. The quantity of solid matter has been found
to vary, within the limits of ordinary health, from 3*6 to 6-7 per cent.;
and the extent of variation in disease is doubtless much greater.
About one-third of the solid matter is made up of alkaline and earthy
salts; and the remainder is made up of organic compounds. The
salts are partly those of the blood, which will not be separated during
the transudation of the serum through the membranous walls of the
Malpighian capillaries, although the albuminous matter is kept back
(§ 196). But there is a much larger proportion of the alkaline and
earthy phosphates in the urine, than is present in the blood ; and this
is liable to a further increase under circumstances to be presently
alluded to.

730. The organic compounds present in the Urinary secretion (in
its healthy state at least), are undoubtedly the result of the waste or
disintegration of the animal fabric; as well as (in certain cases) of the
decomposition of constituents of the blood, which have never under-
gone conversion into organized tissue. Their unfitness to be retained
within the system, is proved by the fatal results which speedily ensue,
when their elimination by the secreting process receives a check; and
also by the crystaline form, in which the most characteristic of them
present themselves, — such a form being altogether incompatible with
the possession of plastic or organizable properties. Of these com-
pounds, the most important, in Man, is that which is named Urea.
It exists in Urine in a state of perfect solution ; and may be readily
separated from it in the form of transparent colourless crystals, which
have a faint and peculiar but not urinous odour. In its ultimate
composition it is identical with Cyanate of Ammonia, being made up
of 2 Carbon, 4 Hydrogen, 2 Nitrogen, and 2 Oxygen, — a formula
much more simple than that of almost any other organic substance.
If we compare its composition with that of Proteine, we shall find that
it contains a far larger proportion of Nitrogen, and far less Carbon
and Hydrogen. Thus, making Oxygen the standard of comparison,
we find that

1 Equivalent of Proteine contains 40 C, 31 H, 5 N, 12 0.
6 Equivalents of Urea contain 12 C, 24 H, 12 N, 12 O.

731. Hence it seems evident, that the great purpose of the Urinary

420 UREA, AND URIC ACID.

excretion is to carry off those products of the metamorphosis of the
azotized tissues, which can neither be set free in the condition of car-
bonic acid and water through the lungs, nor got rid of by the agency
of the liver in the form of solid biliary matter. The amount of Urea
in the Urine is liable to very great variation, in accordance with the
degree in which the disintegrating process has been taking place in
the solid fabric ; and also in conformity with the amount of azotized
matter, which has been taken in as food. Supposing that the latter
were so precisely adjusted to the wants of the system, as to supply
only that which is required for its maintenance, w^e might then mea-
sure the amount of previous waste, by the quantity of Urea present
in the Urine. There can be no doubt as to the fact, that, other things
being equal, the amount of Urea is greatly increased by any unusual
exertion of the Muscular system ; but such an increase cannot be in-
variably, or even usually, attributed to this cause ; since it is equally
certain, that any superfluity in the amount of azotized matter received
into the blood, must be drawn off by the urinary excretion, and thus
that an increase in the quantity of urea may be occasioned by an ex-
cessive use of proteine-compounds as articles of food. The average
proportion of Urea, under ordinary circumstances as to diet and exer-
cise, seems to be from 20 to 35 parts in 1000 ; but it may be raised
to 45 parts by violent exercise, and to 53 parts by an exclusively ani-
mal diet ; whilst it may fall as low as from 12 to 15 parts, when the
dijet is deficient in azotized matter. The total daily excretion of Urea
in adult males seems to average about 430 grains, and that of females
nearly 300 grains; but these averages may be widely departed from,
on the side either of excess or diminution, according to the circum-
stances already noticed. It is interesting to observe, that children of
eight years old excrete, on the average, half qs much Urea as adults;
whilst, in very old persons, the quantity sinks to one-third, or even
less. In proportion to their relative bulks, therefore, children excrete
at least two or three times the quantity of urea, that is set free by
adults ; and four or five times that which is excreted by old persons;
— a fact which corresponds with other indications of the far greater
rapidity of interstitial change in the earlier periods of life, than in
adult or advanced age.

732. There is an organic compound, nearly allied to Urea in com-
position, but differing from it in its distinctly acid properties, and also
in its com>parative insolubility. This substance, termed Uric or Lithic
Acid, forms but a small proportion of the solid matter of Human
Urine in the state of health ; but it is the chief element in the Urine
of the lower Vertebrata; and its presence in too large a proportion is
a frequent source of disease in Man. Its ultimate composition is
10 Carbon, 4 Hydrogen, 4 Nitrogen, 6 Oxygen; it crystalizes in
fine scales of a brilliant white colour and silky lustre ; and it is so
sparingly soluble in water, that at least 10,000 times its own weight
of fluid is required to dissolve it. In healthy Human urine, it is in a
state of perfect solution; but it is precipitated immediately on the ad-

URIC AND HIPPURIC ACIDS. 421

dition of a small quantity of any acid, even the Carbonic: it is evi-
dent, therefore, that it is held in solution by union with some base ;
and according to Liebig, this base is Soda, obtained from the bibasic
Phosphate of Soda, which is present in the urine, and which, by
yielding up a part of its base, gives the acid reaction that is charac-
teristic of the fluid in a healthy state. It is not unfrequently seen,
that the Urine, although clear when voided, deposits Lithic acid when
it is cooled; and this deposit may be due either to the presence of
more Lithic acid than the Phosphate of Soda can take up when cold;
or to the presence of some other acids in the Urine, which set free the
Lithic acid, when the solvent power of the Phosphate is diminished
by the depressed temperature.

733. The amount of Uric acid in healthy Urine does not seem to
be much influenced by the diet, or by the w^aste of the tissues; never
varying much, either by excess or diminution, from 1 part in 1000.
It is liable, however, to be greatly increased in certain disordered
states of the system ; and the surplus, not being kept in solution by
the Phosphate of Soda, is deposited as a sediment, which usually has
a crystaline character, and is tinged of a reddish hue by the colour-
ing matter of the urine. Not unfrequently the Uric acid is deposited
in combination with an alkaline base; and the colour of the sediment
is then usually of a brick-red. Such depositions may take place
directly from the blood ; thus, in attacks of Gout, urate of soda is
separated from the circulating blood, and is deposited in the tissues
around the affected joints, forming the concretions termed " chalk-
stones." There can be no doubt that, when there is a positive ex-
cess of Uric acid in the Urine, it may be generally reduced by dimin-
ishing the quantity of azotized matter in the food ; but when the
deposit is consequent upon the presence of some other acid in the
urine, our treatment should be rather directed to the neutralization of
this, or to the prevention of its formation.

734. There seems reason to believe that we are to regard Hippuric
acid as a normal element of the Urine of Man, although it has been
usually supposed to be restricted to the Herbivorous quadrupeds,
"where it replaces Uric Acid. Its composition and properties are very
different from those of that substance. When pure, it forms long
transparent four-sided prisms; it is soluble in 400 parts of cold water,
and dissolves readily at a boiling heat; and it has a strong acid reac-
tion, with a bitterish taste. It is composed of 18 Carbon, 8 Hydro-
gen, 1 Nitrogen, and 5 Oxygen, w^ith 1 equiv. of Water. When
exposed to a high temperature, or subjected to the putrefactive pro-
cess, it is partly converted into Benzoic acid ; and it is on the presence
of the latter in putrefied Human Urine, that the belief in the existence
of Hippuric acid in the same fluid w^hen fresh, is chiefly grounded.
It is a curious fact, that the administration of Benzoic acid causes
the appearance of a large additional quantity of Hippuric acid in the
Urine; so that its presence is then sufficiently evident. This fact has
been applied to the treatment of disease ; for as the salts of Hippuric

422 OTHER CONSTITUENTS OF URINE.

acid are much more soluble than those of Lithic acid, it is obviously
advantageous to cause the effete crystaline matters, which are de-
stined for elimination from the system, to be discharged as soluble
Hippurates, rather than to be deposited as insoluble Lithates; and it
is asserted by Mr. A. Ure, that he has succeeded, by the administra-
tion of Benzoic acid, in preventing the deposition of Gouty concre-
tions, and even in removing them when they. had been formed.

735. Another acid has usually been regarded, until recently, as
one of the regular constituents of healthy urine, and as* liable to un-
dergo a considerable increase in disease. This is the Lactic; an acid
which is readily formed in Milk, by the metamorphosis of its saccha-
rine elements. But it seems doubtful, from the recent inquiries of
Liebig, whether we are to admit it as a regular constituent of healthy
human Urine; and it appears that a peculiar azotized compound,
which is not entitled to the designation of an acid, but which forms
a definite combination with Zinc, has been mistaken for it. The
amount of this azotized product, and of the compounds it forms
(usually designated as lactic acid and the lactates), has been found
to undergo considerable increase, when the food ingested was alto-
gether destitute of azote, and when the proportion of urea was the
smallest. It would seem as if some of the azotized matter, result-
ing from the disintegration of the tissues, was then discharged in
this form, rather than in that of the more highly azotized compound,
urea.

736. Of the substances ranked under the head of Extractive Mat-
ters, very little is definitely known. They seem to consist, for the
most part, of non-azotized compounds in a state of change ; and their
usual proportion, which is about 10 parts in 1000, has been found to
increase to 16J parts when the diet was exclusively vegetable, and
to diminish to 5 parts when only animal food was ingested.

737. The Urine also contains a considerable amount of Saline
matter, of which the acids as well as the bases are derived from the
mineral kingdom ; and the excretion of them, after they have served
their purpose in the economy, appears to be one of the chief functions
of the Kidney. Of these, a part may find their way directly into the
urine from the serum of the blood, when its water is being filtered off
(so to speak) through the walls of the Malpighian capillaries ; for
although, from the peculiar properties of animal membranes (§ 196),
the albuminous constituents of the serum are held back, the saline
matter, which is in a state of perfect solution, must pass with the
water. This is probably the chief source of the large quantity of the
muriates of soda and ammonia contained in the urine. But the
Urinary secretion seems to be specially destined to eliminate the saline
compounds, which are formed by the acidification of the Sulphur and
Phosphorus, taken in with the proteine-compounds as food. These
substances are united with Oxygen in the system, and are thus con-
verted into Sulphuric and Phosphoric acids; w^hich acids unite with
alkaline bases, that were ingested in combination with Citric, Tartaric,

»

SALTS OF THE URINE. 423

Oxalic, and other organic acids; the latter undergoing decomposition
within the system, and leaving the bases ready to unite with others.
Such weakly combined bases abound in the food of Herbivorous ani-
mals ; and their urine is almost invariably alkaline^ the quantity of the
Sulphuric and Phosphoric acids generated in the system not being
sufficient to neutralize it. On the other hand, they are nearly absent
in the food of the Carnivora; and their urine is therefore almost inva-
riably acid^ from the want of neutralization of the Sulphuric and
Phosphoric acids.

738. The Alkaline Sulphates^ whether taken in as such, or formed
in the manner now described, are soluble enough to be always passed
off in a fluid form ; but this is not uniformly the case with the Phos-
phates, which are frequently deposited as sediments of a dead-white
aspect, sometimes crystaline, and sometimes wholly or partly amor-
phous. The crystaline sediment consists of the triple phosphate, or
phosphate of ammonia and magnesia ; the amorphous contains an ad-
mixture of the phosphate of lime. The urine, when these are depo-
sited, is usually alkaline, sometimes very decidedly so ; and there is
reason to think that, in many cases, this alkaline character, and the
deposit of phosphatic sediments, are due to an alkaline secretion from
the walls of the bladder and urinary passages, which result from an
irritable state nf their membrane, — the urine, as secreted by the kid-
ney, having its usual properties.* That an alkaline condition of the
urine, resulting from the presence of an unusual amount of bases, is
capable of producing a phosphatic deposit, is shown by the simple
experiment of adding ammonia to healthy urine, which will occasion
a precipitation of the triple phosphate.

739. But there can be little doubt, that a frequent cause of the
deposit is excessive production of the phosphatic salts, arising from
the increased waste or disintegration of Nervous matter, which takes
place when it is in a state of unusual activity, either from intense
thought, from prolonged exertion, or from continued anxiety. The
general principles already set forth, in regard to the dependence of
the functional activity of the Nervous Centres upon a supply of arte-
rialized blood (§ 384), show the probability that every act of theirs
involves the oxygenation of a certain quantity of nervous matter. In
this oxygenation, phosphoric acid will be produced, from the large
amount of phosphorus contained in the nervous matter ; and this will
unite in part with ammonia, which is perhaps set free by the same
metamorphosis, or is derived from other sources; and in part with
bases derived from the food. The experience of every studious man
must have shown him (if he make any observations on the matter at
all) the frequent coincidence between the presence of phosphatic
deposits in his urine, and an excess of mental labour ; and there are
many instances on record, in which the periodical recurrence of the

* See Dr. G. O. Rees on the Analysis of the Blood and Urine in Health and Dis-
ease, 2d Ed. p. 136.

424 DISORDERED STATES OF THE URINARY SECRETION.

latter has been so invariably followed by the recurrence of the former,
that no reasonable doubt can exist as to their mutual connection.

740. It is very important, for the successful treatment of those
Urinary deposits, which consist of the normal elements of the Urine,
— namely, Lithic Acid, and the Phosphates, — that the leading facts
already stated should be borne continually in mind. In the first place,
these sediments may depend upon the general condition of the fluid,
and not upon any excess in the constituents of which they are com-
posed ; thus a lithic deposit may result from the presence of an excess
of some other acid in the urine ; and a phosphatic sediment may be
produced by the excess of bases. In such cases, then, our treatment
should be directed, not to diminish the quantity of the peculiar con-
stituents of the deposits, but to rectify the state of the Urine on which
their precipitation depends. But, in the second place, the sediments
may be present in such great amount, as to indicate that their consti-
tuents are present in the urine to an excessive degree ; and our treat-
ment must then be directed towards the diminution of the quantity
produced. Thus the tendency to lithic acid deposit may be frequently
cured, by simply diminishing the quantity of azotized matter in the
food ; and the undue formation of the phosphates may be often kept
in check by that mental repose, which is peculiarly required after
long-continued and severe exercise of the intellectual faculties, or
strong excitement of the feelings.

741. There is no doubt whatever, that the total suspension of the
Urinary secretion is productive of rapidly fatal results, from the accu-
mulation of the elements of the secretion in the blood ; and it would
appear that the tissue on which their presence in the circulating fluid
exerts the most injurious effects, is the Nervous. It is probable that
Urea is the substance, which is most directly concerned in producing
the noxious influence ; and we see an effort made by the system (so to
speak) to get rid of it, in those cases in which a discharge of urinous
fluid takes place by unusual channels, such as from the mucous mem-
brane of the stomach, the mamma, the umbilicus, the nose,&c., w^hen
the usual secreting action of the Kidney has been suspended. Al-
though the accounts of such cases have been treated w^th ridicule by
some Physiologists, yet there seems no valid reason to discredit them,
when it is borne in mind that, in persons who have died from the
complete suspension of the secretion, effusions containing urea have
been found in the serous cavities of the trunk, and in the ventricles of
the brain. The poisonous influence of an accumulation of urea in the
blood, when strongly exerted, produces, in the first instance, irregular
or convulsive movements, which are dependent upon irritation of the
Spinal system of nerves; then loss of consciousness, depending upon
the suspension of the powers of the Brain ; and, lastly, complete sus-
pension of the powers of the spinal system, so that the ordinary reflex
actions cease, and life becomes extinct from the stoppage of the re-
spiratory movements (§ 688). There is reason to believe that many
convulsive motions, for which no obvious cause can be assigned, have

CUTANEOUS GLANDULE.

425

their origin in a disordered condition of the blood, resulting from im-
perfect elimination of Urea; thus it has been ascertained that, in seve-
ral cases of puerperal convulsions, urea was present in the blood ; the
functional power of the kidney being diminished by chronic disease.
It is especially to be noticed, that most of the cases in which the
urinary secretion is discharged through some irregular channel, occur
in persons who have been subject to those convulsive affections, which
are commonly designated as hysterical; and that the discharge of a large
quantity of urine through the natural channel, is often the termination
of an hysterical paroxysm. It is desirable, therefore, that in all such
obscure cases, the state of the urinary secretion should be carefully
looked to.

Fig. 126.

I

4. Of the Cutaneous and Intestinal Glandulce.

742. The Glandulae which are disposed in the substance of the
Skin, and in the walls of the Intestinal canal, although individually,
minute, make up by their aggregation an excreting apparatus of no
mean importance. The Skin is

the seat of two processes in parti-
cular ; one of which is destined to
free the blood of a large quantity
of fluid ; and the other to draw
off a considerable amount of solid
matter. To effect these processes,
w^e meet with two distinct classes
of glandulae in its substance ; the
Sudoriparous or sweat-glands ;
and the Sebaceous or oil-glands.
They are both formed, however,
upon the same simple plan ; and
can frequently be distinguished
only by the nature of their secreted
product.

743. The Sudoriparous or per-
spiratory glandules form small oval
or globular masses, situated just
beneath the cutis, in almost every
part of the surface of the body.
Each is formed by the convolu-
tion of a single tube; which thence
runs towards the surface as the
efferent duct, making numerous
spiral turns in its passage through
the skin, and penetrating the epi-
dermis rather obliquely, so that its
orifice is covered by a sort of little
valve of scarf-skin, which is lifted

The anatomy of the skin. 1. The epidermis,
showing the oblique laminae of which it is com-
posedj and the imbricated disposition of the ridges
upon Us surface. 2. The rete mucosum or deep
layer of the epidermis 3. Two of the quadrila-
teral papillary clumps, such as are seen in the
palm of the hand or sole of the foot; they are
composed of minute conical papillae. 4. The
deep layer of the cutis, the corium. 5. Adipose
cells. 6. A sudoriparous gland with its spiral
duct, such as is seen in the palm of the hand or
sole of the foot. 7. Another sudoriparous gland
with a straighter duct, such as are seen in the
scalp. 8. Two hairs from the scalp, enclosed in
their follicles; their relative depth in the skin is
preserved. 9. A pair of sel)aceous glands, open-
ing by short ducts into the follicle of the hair.

426

VARIATIONS IN CUTANEOUS EXHALATION.

up as the fluid issues from it. The convoluted knot, of which the
gland consists, is copiously supplied with blood-vessels. On the
palm of the hand, the sole of the foot, and the extremities of the
fingers, the apertures of the perspiratory ducts are visible to the naked
eye, being situated at regular distances along the little ridges of sen-
sory papillae, and giving to the latter the appearance of being crossed
by transverse lines. According to Mr. Erasmus Wilson, as many as
3528 of these glandulae exist in a square inch of surface on the palm
of the hand ; and as every tube, when straightened out, is about a
quarter of an inch in length, it follows that in a square inch of skin
from the palm of the hand there exists a length of tube equal to 882
inches, or 73J feet. The number of glandulse in other parts of the
skin is sometimes greater, but generally less than this ; and according
to Mr. Wilson, about 2800 inches may be taken as the average num-
ber of pores in each square inch throughout the body. Now the
number of square inches of surface, in a man of ordinary stature, is
about 2500 ; the number of pores, therefore, is seven millions ; and
the number of inches of perspiratory tubing would thus be 1,750,000;
or 145,833 feet ; or 48,611 yards ; or nearly 28 miles.

744. From this extensive system of glandulse, a secretion of watery
fluid is continually taking place; and a considerable amount of solid
matter also is drawn off by the epithelium-cells that line the tubuli.
Under ordinary circumstances, the fluid is carried off in the state of
vapour, forming the insensible perspiration ; and it is only when its
amount is considerably increased, or when the surrounding air is
already so loaded with moisture as to be incapable of receiving more,
that the fluid remains in the form of sensible perspiration upon the sur-
face of the skin. It is difiicult to estimate the proportion of solid
matter contained in this secretion ; partly on account of the great
variations in the amount of fluid eliminated by the Sudoriparous
glands, which are governed by the temperature of the skin ; and
partly because the secretion can scarcely be collected for analysis,
free from the sebaceous and other matters which accumulate on the
surface of the skin. According to Anselmino it varies from \ to IJ
per cent.; and consists in part of lactic acid, to which the acid reac-
tion and sour smell of the secretion are due ; in part of a proteine-
compound, which is probably furnished by the epithelium-cells that
line the tubes ; and in part of saline matters, directly proceeding from
the serum of the blood.

745. The amount of fluid excreted from the skin is almost entirely
dependent upon the temperature of the surrounding medium ; being
increased with its rise, and diminished with its fall. The object of
this variation is very evident ; being the regulation of the temperature
of the body. When the surface is exposed to a high degree of external
heat, the increased amount of fluid set free from the perspiratory
glands becomes the means of keeping down its own temperature ; for
this fluid is then carried off in a state of vapour, as fast as it is set
free ; and in its change of form, it withdraws a large quantity of caloric

SUPPRESSED EXHALATION. ^ 427

from the surface. But if the hot atmosphere be already loaded with
vapour, this cooling power cannot be exerted ; the temperature of the
body is raised ; and death supervenes, if the experiment be long con-
tinued. The cause of the increased secretion is probably to be looked
for in the increased determination of blood to the skin, which takes
place under the stimulus of heat. — The entire loss by Exhalation from
the lungs and skin, during the twenty-four hours, seems to average a
little above 2 lbs. In a warm dry atmosphere, however, it has been
found to rise to as much as 5 lbs. ; whilst in a cold damp one, it may
be lowered to If lb. Of this quantity, the pulmonary exhalation is
usually somewhat less than one-third, and the cutaneous somewhat
more than two-thirds ; but when the quantity of fluid lost is unusually
great, the increase must be chiefly in the Cutaneous exhalation ; since,
as already pointed out (§ 701), the amount of exhalation from the
lungs is not influenced by the external temperature, but only by the
degree in which the surrounding air is previously saturated with
moisture.

746. The variations in the amount of fluid set free by Cutaneous
and Pulmonary Exhalation, are counterbalanced by the regulating
action of the Kidney ; which allows a larger proportion of water to be
strained off in a liquid state from the blood-vessels, as the Exhalation
is less, — and vice versa. The Cutaneous and tJrinary excretions
seem to be vicarious, not merely in regard to the amount of fluid
which they carry off' from the blood ; but also in respect to the solid
matter which they eliminate from it. It appears that at least 100
grains of effete azotized matter are daily thrown off* from the skin ;
and any cause which checks this excretion, must increase the labour
of the Kidneys, or produce an accumulation of noxious matter in the
blood. Hence attention to the functions of the skin, at all times a
matter of great importance, is peculiarly required in the treatment of
Urinary diseases ; and it will be often found that no means is so useful
in removing the lithic acid deposit, as copious ablution and friction
of the skin, combined with exercise. When the Exhalant action of
the skin is completely checked, by the application of an impermeable
varnish, the eff*ect is not (as might be anticipated) an elevation of the
temperature of the body ; on the contrary it is lowered, in conse-
quence, as it would appear, of the interruption to the aeration of the
blood through the skin, which is a function of such importance in the
lower animals (§ 671), and of no trifling account in Man; and in a
short time, a fatal result ensues. A partial suppression by the same
means gives rise to febrile symptoms, and to Albuminuria, or escape
of the albuminous part of the liquor sanguinis into the urinary tubes,
in consequence (it would appear) of the increased determination which
then takes place towards the kidneys. These facts are interesting, as
throwing light upon the febrile disturbance, which accompanies those
cutaneous diseases, that affect the whole surface of the skin at once,
and interfere with its functions ; and as accounting also for the Albu-

J^ SEBACEOUS GLANDS.

minuria, which frequently manifests itself during their progress, espe-
cially in Scarlatina.

747. The Skin is likewise furnished with numerous Sebaceous
glands, which are distributed more or less closely over the whole
surface of the body ; being least abundant where the Perspiratory
glandulse are most numerous; and vice versa. They are altogether
absent on the palms of the hands and the soles of the feet ; and are
particularly frequent in the skin of the face, and in the scalp. They
difier greatly in size and in degree of complexity; sometimes con-
sisting of short straight follicles ; sometimes closely resembling the
Sudoriparous glandulse, the tubes, however, being usually straighter
and wider; and being sometimes much more complex in structure,
consisting of a number of distinct sacculi clustered round the extremity
of a common duct, into which they open, and forming little arborescent
masses, about the size of millet seeds. In some situations they ac-
quire still greater complexity. Thus the Meibomian glandulse, which
are found at the edge of the eyelids, and which secrete an unctuous
matter for their lubrication, are long sacculi branching out at the sides
(Fig. 107); and the glandulse of the ear passage, which secrete its
cerumen or waxy matter, and which belong to the general Sebaceous
system, are formed of long tubes, highly contorted, and copiously sup-
plied with blood-vessels. In the hairy parts of the skin, we usually
find a pair of Sebaceous follicles opening into the passage through
which every hair ascends (Fig. 126, 9). The purpose of the seba-
ceous secretion is evidently to prevent the skin from being dried
and cracked by the influence of the sun and air. It is much more
abundant in the races of mankind, which are formed to exist in warm
climates, than in the races that naturally inhabit cold countries ; and
the former are accustomed to aid its preservative power, by lubri-
cating their skin with vegetable oils of various kinds; which process
they find to be of use in protecting it from the scorching influence of
the solar rays. — The Sebaceous follicles are frequently the residence
of a curious parasite, the Bemodex folliculorum ; which is stated by
Mr. Erasmus Wilson to be present in great numbers in the skin of
almost all inhabitants of large towns ; the activity of their cutaneous
glandular system being much checked, by the want of free exposure
to pure air, and by inert habits of life.

748. To what extent the Sebaceous secretion can be regarded as
destined to free the Blood from deleterious matters, it may not, per-
haps, be very easy to say; but with regard to the functions of the skin
taken altogether, as a channel for the elimination of morbific matters
from the blood, it is probable that they have been much underrated ;
and that much more use might be made of it, in the treatment of dis-
eases,— especially of such as depend upon the presence of some mor-
bific matter in the circulating current, — than is commonly thought
advisable. We see that Nature frequently uses it for this purpose ; a
copious perspiration being often the turning-point or crisis of febrile
diseases, removing the cause of the malady from the blood, and

ELIMINATING ACTION OF THE SKIN. 429

allowing the restorative powers free play. Again, certain forms of
Rheuraatism are characterized by copious acid perspirations ; and
instead of endeavouring to check these, we should rather encourage
them as the best means of freeing the blood from its undue accumu-
lation of lactic acid. And it is recorded that in the " sweating sick-
ness," which spread throughout Europe in the 16th century, no re-
medies seemed of any avail but diaphoretics ; which, aiding the powers
of nature, concurred with them to purify the blood of its morbific
matter. The hot-air bath, in some cases, and the wet sheet (which,
as used by the Hydropathists, is one of the most powerful of all dia-
phoretics), will be probably employed more extensively as therapeutic
agents, in proportion as the importance of acting on the skin, as an
extensive collection of glandulse, comes to be better understood.
The absurdity of the "Hydropathic" treatment consists in its indis-
criminate application to a great variety of diseases ; no person, who
has watched its operation, can deny that it is a remedy of a most
powerful kind ; and if its agency be fairly tested, there is strong rea-
son to believe, that it will be found to be the most valuable curative
means we possess for various specific diseases, which depend upon
the presence of a definite " materies morbi" in the blood, especially
Gout and chronic Rheumatism ; as well as for that depressed state of
the general system, which results from the "wear and tear" of the
bodily and mental powers.

749. The Mucous surface of the Alimentary Canal is furnished,
like the skin, with a vast number of glandulee, varying in complexity,
from the simple follicle, to a mass consisting of numerous lobules
opening into a common excretory duct. The functions of these, as
already pointed out, are equally various. The simple follicles ap-
pear destined, for the most part, to secrete the protective mucus, which
intervenes between the membranous wall and the substances contained
in the canal, and which serves to protect the former from the irritat-
ing action of the latter. The more complex follicles of the Stomach
elaborate the Gastric fluid, which is the prime agent in the digestive
process (§ 496). But there is strong reason to believe, that the func-
tion of the numerous glandulse, which beset the walls of the small
intestine, and which are known as Brunner's and Peyer's glands
(after the names of their discoverers), is purely excretory ; and that
they are destined to eliminate putrescent matters from the blood, and
to convey them, by the readiest channel, completely out of the body.
That the putrescent elements of the feces are not immediately de-
rived from the food taken in, so much as from the secreting action
of the intestinal glandulse, appears from this consideration ; — that
fecal matter is still discharged, even in considerable quantities, long
after the intestinal tube has been completely emptied of its alimentary
contents. We see this in the course of many diseases, when food is
not taken for many days, during which time the bowels are com-
pletely emptied of their previous contents by repeated evacuations ;
and whatever then passes, must be derived from the intestinal walls

430 GENERAL RELATIONS OF EXCRETING PROCESSES.

themselves. Sometimes a copious flux of putrescent matter con-
tinues to take place spontaneously ; whilst it is often produced by the
agency of purgative medicine. The " colliquative diarrhoea," which
frequently comes on at the close of exhausting diseases, and which
usually precedes death by starvation, appears to depend, not so much
upon a disordered state of the intestinal glandul8e, as upon the gene-
ral disintegration of the solids of the body, which calls them into ex-
traordinary activity, for the purpose of separating the decomposing
matter.

750. Thus we perceive, that we have here, also, to watch for the
indications of Nature ; and that this extensive system of intestinal
glandulse, being the principal channel for the elimination of putres-
cent matters from the blood, should be especially attended to, when
there is reason to think that such matters are present in too large an
amount. Hence, when diarrhoea is already existing, we may often
do more good by allowing it to take its course, or even by increasing
it by the agency of purgative medicines, than by attempting to check
it, and thus causing the retention of the morbid matter in the circu-
lating current. But, on the other hand, it is necessary to bear in mind
the extreme irritability of the intestinal raucous membrane ; and care-
fully to avoid exciting it, when it is already in excess, or when there
is danger that it will supervene, — as in that form of Fever in which
there is a peculiar liability to inflammation and ulceration of the walls
of the alimentary canal.

5. General Summary of the Excreting Processes.

751. We have now passed in review the various processes, by
which the products of the disintegration of the animal tissues are car-
ried off*; and we have seen that the necessity for their removal is
much more urgent than for their replacement. A cold-blooded animal
may subsist for some weeks, or even months, without a fresh supply
of food ; the waste of its tissues being so small, if it remain in a state
of rest, as to be quite compatible with the continuance of its life ; and
a warm-blooded animal may live for many days or even weeks, pro-
vided that it has in its body a store of fat sufficient to keep up its
heat by the combustive process. But in either case, if the exhalation
of carbonic acid by the lungs, the elimination of biliary matter by the
liver, the separation of urea or uric acid by the kidneys, or the with-
drawal of putrescent matter by the intestinal glandule, be completely
checked, a fatal result speedily ensues; — more speedily in warm-
blooded animals than in those which cannot sustain a high inde-
pendent temperature, on account of the greater proneness to decom-
position in the bodies of the former, than in those of the latter; — and
more speedily in the latter, when their bodies are kept at an elevated
temperature by the warmth of the surrounding medium, than when
the degree of heat is so low, that there is little proneness to sponta-
neous change in the substance of their bodies.

RELATIONS OF BILIARY AND PULMONARY EXCRETIONS. 431

752. It may be taken as a general principle, in regard to the
Excreting processes (including Respiration), that they have a three-
fold purpose ; — in the first place, to carry off the normal results of the
waste or disintegration of the solid tissues, and of the decomposition
of the fluids; in the second place, to draw off the superfluous aliment-
ary matter, which, though received into the circulating current, is
not converted into solid tissue, in consequence of the want of demand
for it ; — and in the third place, to carry off the abnormal products,
which occasionally result from irregular or morbid changes in the
system. Thus by the Lungs are excreted a large amount of carbon,
and some hydrogen, resulting from the disintegration of the tissues,
especially the nervous and muscular; the same elements in animals
that take in a large proportion of farinaceous or oleaginous aliment,
may be derived immediately from the food, without any previous
conversion into solid tissue ; and there can be little doubt that the
respiratory function is also an important means of purifying the blood
from various deleterious matters, either introduced from without (such
as narcotic poisons), or generated within the body (such as the poison
of fever*). And it is important to bear this last circumstance in mind ;
since it enables us to understand how, if time be given, the system

frees itself from such noxious substances ; and points out the duty of
the medical attendant to be rather that of supporting the powers of
the body by judiciously devised means, and of aiding the elimination
of the morbid matter through the lungs and skin by a copious supply
of pure air, than of interfering more actively to promote that which
Nature is already effecting in the most advantageous manner.

753. In like manner, the Liver is charged with the separation of
hydrocarbon, in a fluid form ; for which a supply of oxygen is not
requisite. This product is partly derived from the waste of the sys-
tem; but the arrangement of the biliary vessels leads to the belief,
that much of it is at once derived from crude matter, taken up by the
mesenteric veins, and eliminated from them by the hepatic cells,
without ever passing into the general circulation. And various facts
seem to indicate, that the Liver is also destined to remove from the
blood extraneous substances, which are noxious to it. Thus, in cases
where death has resulted from the prolonged introduction of the salts
of Copper into the system, a considerable amount of that metal has
been obtained from the substance of the gland. — It has been already
pointed out (§ 720) that the Liver and Respiratory organs are deve-
loped in an inverse proportion to each other, in the different classes
of animals ; the Liver being largest where the respiration is most
feeble, and vice versa. Now it is important to bear in mind, that the
functional activity of the liver in any individual must be in like
manner the greater, as the amount of respiration is less ; the hydro-

* There is strong reason to believe that, in many instances, a small amount of
poisonous matter introduced from without, in the form of a contagion or miasm, may
lead, by a process resembling fermentation, to the production of a large quantity of
similar noxious substances in the animal fluids.

432 DEPURATING ACTION OF THE KIDNEYS.

carbon, which is eliminated by the lungs, when their activity is the
greatest, being thrown upon the liver for separation, when the respi-
ration is feeble. We have seen that the amount of carbonic acid
exhaled at high temperatures, is much less than that set free in a
colder atmosphere ; consequently, the liver is called upon to do more
in warm climates, and is therefore peculiarly liable to disordered
action, — unless the diet be carefully regulated, in accordance with the
wants of the system.

754. The effects of diminished respiration, in producing an increase
in the fatty constituents of the liver, are peculiarly well marked in the

diseased condition produced in the geese, that are
Fig. 127. being prepared for celebrated Strasburg pates. The

unfortunate bird is closely confined at a high tem-
perature ; so that the respiration is reduced to its
minimum amount by the combined effects of warmth
_ and muscular inaction ; and it is then crammed with
ged^^with Faf:-°a, maizc, which contains a large amount of oily matter.
So'^sl' globules.'' ^' The consequence is, that its liver soon enlarges, and
becomes unusually fatty ; its cells being gorged with
oil-globules, instead of each containing no more than one or two : and
it is then ready for the epicureans who set so high a value on the
pate defoie gras. A similar diseased condition of the liver frequently
presents itself in Man, as a consequence of chronic disorders of the
respiratory organs, which diminish the amount of hydrocarbon elimi-
nated through their agency ; this " fatty liver" is peculiarly common
in the advanced stages of Phthisis.

755. With regard to the Kidneys, it has been already pointed out
that they are the special emunctories of the azotized products of the
decomposition of the tissues ; and that they serve also to convey away
the overplus of such earthy and alkaline salts, as are readily soluble.
Moreover, it has been shown that the surplus proteine-compounds,
which are not required for the nutrition of the system, must be ex-
creted by their agency, after having been metamorphosed into urea.
And we have now to notice, that other matters of an injurious charac-
ter, whether introduced from without, or generated within the sys-
tem, are drawn off by the same channel. Thus the saline compounds,
taken up by the absorbent process (§ 493), are for the most part set
free through these organs ; especially when their properties are such,
as to excite the action of the kidneys in a peculiar degree. Thus,
Prussiate of Potash has been detected in the urine, within two mi-
nutes after it had been introduced into the stomach. It has been
sometimes noticed that Iodide of Potassium, when administered as
a medicine, is retained w^ithin the body for some days, producing ex-
tensive cutaneous eruptions, or some other unusual consequence; and
that it then suddenly begins to pass off by the kidneys, and is ex-
creted in very large quantities. The effect of the inhalation of the
vapour of turpentine, even in a very diluted state, in speedily
imparting to the urine the odour of violets, is an evidence that not

DEPURATING ACTION OF SKIN, ETC. 433

merely the actual substances imbibed, but new and peculiar com-
pounds to which they give rise, are thus eliminated by the Kidneys.

756. The most singular variations in the excretory function of the
Kidneys are seen, however, when the Urine is charged with sub-
stances which are not only foreign to it, but are altogether foreign
to the healthy body. The most remarkable instance of this is seen
in the disease termed Diabetes, in which a large quantity of Sugar is
formed, either directly from the food, or by the disintegration of the
solid tissues ; and in which this compound is eliminated by the Kid-
neys, imparting to the urine a saccharine taste. And another example
of the same general fact is seen in the "oxalic diathesis," in which
an unusual arrangement of the elements, that usually form urea or
uric acid, gives rise to a new and peculiar compound, oxalate of am-
monia; this being drawn off' by the kidneys, and being decomposed
by the calcareous matter present in the urine, gives rise to a deposit
of oxalate of lime. In the treatment of such diseases, our attention
must be given, not so much to the secreting organ, as to the condition
of the system at large, of which the character of the secreted product
is the indication or exponent.

757. To what has already been stated in regard to the exhalant
functions of the Lungs and Skin, it may be added that many states
of disease are marked by an unusual odour emitted from the body;
and there can be little doubt that the peculiar odorous matter is pre-
formed in the blood, — as we know that the ordinary scent of any
species (whether Man, Dog, Horse, Goat, &c.,) may be set free from
the blood of that species, by the addition of sulphuric acid. The ex-
istence of such odours, therefore, is not to be attributed to disordered
function in the excreting organs ; but to the formation of morbid pro-
ducts in the interior of the body, which these organs do their best to
remove. The fetid breath, which frequently accompanies an attack
of indigestion, is another instance of the power of the lungs to eli-
minate not merely Carbonic acid, but other products of the changes
in composition, which the food undergoes when introduced into the
system.

758. The same remarks apply, and with yet greater force, to the
intestinal glandulse ; whose function it is, not merely to remove the
putrescent matter ordinarily formed by the disintegration of the tis-
sues, or by the decomposition of unassimilated food, but also to draw
off* the still more offensive products of such changes as take place in
disease. Thus there are conditions of the system, in which, without
any well-marked disorder, the feces emit a peculiarly fetid odour ;
and with these is almost always associated a depressed state of mind.
Now it can scarcely be doubted, that the real fault is here rather in
the early part of the nutritive operations, than in the excretory func-
tion; and that the fetor of the contents of the intestine depends upon
the undue formation of putrescent naatter in the system, which, by
tainting the blood, causes its action upon the brain to become un-
healthy. The object of the physician will be here to eliminate the

28

434 HEAT OF ANIMALS AND PLANTS.

morbid product, by the moderate use of purgatives ; and so to regu-
late the diet and regimen, as to correct the tendency to its formation.
— An excessive fetor in the evacuations, as well as in the exhalations
from the skin and lungs, is peculiarly characteristic of those very se-
vere forms of typhus (now, happily, of comparatively rare occurrence),
which are termed putrid fevers. Here the whole of the solids and
fluids of the body appear to have an unusual tendency to decomposi-
tion, in consequence of the introduction of some morbid agent, which
acts as a ferment; and the system attempts to free itself from the pro-
ducts of that decomposition, by the various organs of excretion, par-
ticularly the Skin and intestinal surface.

759. It is of great importance that the Student should form clear
conceptions on this subject; and that he should not (as too often
happens), by directing his remedies to the mere symptoms or results
of a disease, act in precise opposition to the natural tendency of the
system to free itself from some unusual noxious matter, through those
channels which are ordinarily destined to carry off only the regular
products of its disintegration.

CHAPTER X.

OF THE DEVELOPMENT OF HEAT, LIGHT, AND ELECTRICITY IN THE
ANIMAL BODY.

760. It has been shown, in an earlier part of this volume (Chap.
II.), that all Vital actions require a certain amount of Heat for their
performance ; and that there is a great variety amongst the different
classes of Animals, both in regard to the degree of Heat which is
most favourable to the several processes of their economy, and in
regard to their own power of sustaining it, independently of oscilla-
tions in the temperature of the surrounding medium. As a general
rule, the Invertebrated animals are cold-blooded ; that is, they have
little or no power of sustaining an independent temperature. The
degree of energy of their vital actions entirely depends, therefore,
upon the Avarmth they receive from the air or water they inhabit; they
have no power of resisting the depressing influence of cold ; and they
are generally so organized, as to pass into a state of complete inaction
or torpidity, when the temperature sinks below a certain point, — after
gradually becoming more and more inert with every diminution in the
heat of their bodies. The same is true, also, of most Fishes and
Reptiles : but the animals of the former class, from the more equable
temperature of the medium they inhabit, are not so liable to be re-
duced to inaction as the latter ; being usually so organized, as to retain
their activity so long as the water around them continues liquid ; and

HEAT OF ANIMALS AND PLANTS. 435

being actually imbedded in a frozen state, when the water around
them is converted into ice, without the loss of their vitality. There
are certain Fishes, however,-r-such as the Tunny, Sword-fish, and
other large species of the Mackarel tribe, — which are able to sustain
a temperature considerably above that of the sea they inhabit ; thus
in the Bonito, the heat of the body has been found to be 99°, when
the temperature of the surrounding sea was but 80^°. It is not pro-
bable, however, that the temperature of the body would be kept up
to the same standard, if that of the sea should be considerably low-
ered ; but it would probably remain at from 18° to 20° above the latter.
And in like manner, it has been noticed that many of the more active
Reptiles possess the power of sustaining the temperature of their
bodies at 10° or 15° above that of the surrounding air.

761. The classes of animals, which are especially endowed with
the power of producing and maintaining heat, are Insects, Birds, and
Mammalia. The remarkable variations which present themselves in
the temperature of the first of these classes, and the connection of
these variations with the condition of the animals, in regard to ac-
tivity or repose, have already been sufficiently noticed (§ 123). — The
temperature of Birds is higher than that of any other class of ani-
mals; varying from 100° to 111° or 112°. The lowest degree is
found in some of the aquatic species, as the Gull, and in those which
principally live on the ground, as the Fowl tribe ; and the highest in
the birds of most active flight, as the Swallow. The temperature of
the Mammalia seems to range from about 96° to 104°; that of Man
has been observed as low as 96J°, and as high as 102°. The varia-
tions are dependent in part upon the temperature of the external air;
but are influenced also by the general condition of the body, as to
repose or activity, the period of the day, the time that has elapsed
since a meal, &c. A somewhat larger amount of caloric is generated
during the day, than in the night ; and the body is usually warmer,
by a degree or two, at noon, than at midnight. There is also a slight
increase during the digestion of a meal; and exercise is a powerful
means of raising the temperature. — The range of temperature is much
greater in disease ; thus the thermometer has been seen to rise to 106°
in Scarlatina and Typhus, and to 110f° in Tetanus; whilst it has
fallen to 82° in Spasmodic Asthma, and to 77° in Cyanosis and Asiatic
Cholera.

762. In searching for the conditions, on which this production of
heat within the Animal body is dependent, it is very important to
bear in mind, that a similar generation of Caloric may be observed
in the Vegetable kingdom. It appears from the most recent and
exact experiments, that all living Plants are somewhat warmer than
similar dead plants exposed to the same atmosphere ; and that the
elevation is the greatest in the leaves and young stems, in which the
most active vital changes are taking place. But the most decided
production of heat occurs in \he flowering of certain Plants, such as
the Arum, which have large fleshy receptacles, on which a great

436 CONDITIONS OF DEVELOPMENT OF HEAT.

number of blossoms are crowded ; thus a thermometer placed in the
centre of five spadixes of the Arum cordifolium has been seen to
rise to lll°; and one placed in the midst of twelve spadixes has risen
to 121°; whilst the temperature of the surrounding air was only Q>Q°,
In the germination of seeds, also, a great elevation of temperature
occurs; which is rendered most evident by bringing together a num-
ber of seeds, as in the process of malting^ so that the caloric is not
dissipated as fast as it is generated ; the thermometer, placed in the
midst of a mass of seeds in active germination, has been seen to rise
to 110°.

763. Thus it is evident that the chemical changes, which are in-
volved in the operations of Nutrition, are capable of setting free a
large amount of heat ; which, although ordinarily dissipated from
tiie vegetating surface too speedily to manifest itself, becomes sensible
enough, when this rapid loss is checked. If we further examine into
the nature of the chemical changes, which appear most concerned in
this elevation of temperature, we find that they uniformly consist in
the combination of the carbon of the plant with the oxygen of the
atmosphere; so that a large quantity of carbonic acid is formed and
set free, precisely in the manner of the Respiration of Animals. This
process is so slowly performed, in the ordinary growth of Plants, that
it is concealed (as it were) by the converse change, — Xh^ fixation of
carbon from the carbonic acid of the atmosphere, under the influence
of light (§ 83). But it takes place with extraordinary energy during
flowering and germination; a large quantity of carbon being set free,
'by union with the oxygen of the air ; and the starchy matter of the
Teceptacle, or of the seed, being converted into sugar. Now it has
been ascertained by careful experiments, that the amount of heat gene-
rated is in close relation with the amount of carbonic acid set free;
and that, if the formation of the latter be prevented, by placing the
flower or the seed in nitrogen or hydrogen, no elevation of tempera-
ture takes place ; whilst if the process be stimulated by pure oxygen,
so that a larger proportion of carbonic acid is evolved, the elevation
of temperature is more rapid and considerable than usual.

764. Upon examining into the conditions under which Caloric is
generated in the Animal body, we find them essentially the same.
Wherever the temperature of the body is maintained at a regular
standard, so as to be independent of variations in the warmth of the
surrounding medium, we find a provision for exposing the blood most
freely to the influence of oxygen, and for extricating its carbonic acid ;
thus in Birds and Mammals, the blood is distributed, in a minute ca-
pillary network, on the walls of the pulmonary air-cells, the gaseous
contents of which are continually renewed ; and in Insects, the air is
carried into every part of the body, by the ramifying trachese. We
constantly find a proportion between the amount of heat evolved, and
that of carbonic acid generated ; this is peculiarly evident in Insects,
whose respiration and calorification vary so remarkably (§ 123); but
it is also proved by comparing the amount of carbonic acid generated

CONDITIONS OF DEVELOPMENT OF HEAT, 437

by warm-blooded animals, when the external temperature is low, and
when more heat must be evolved to keep the temperature of their
bodies up to its proper standard, with that generated by the same
animals in a warmer atmosphere, when the proper animal heat is
diminished in amount (§ 691).

765. The sources of the Carbonic Acid thrown off by the lungs,
have been already pointed out (Chap. VIII.): it is partly derived
from the metamorphosis of the tissues; but partly, in all but purely
carnivorous animals, more directly from the non-azotized portion of
the food. The precise mode in which the carbon of this is united
with the oxygen derived from the atmosphere, is not yet known ; but
it is certain that, in whatever manner the combination takes place, a
certain measure of caloric must be generated. It appears, however,
from various experiments, that the whole quantity of caloric gene-
rated by an animal in a given time, is greater than that which would
be evolved by the combustion of the carbon, included in the carbonic
acid evolved during the same time. Hence it is evident that other
chemical processes occurring within the body are concerned in the
maintenance of the temperature ; and it is not difficult to point to
some of these. It is probable, in the first place, that some of the
hydrogen of the food may be " burned off" by union with the oxygen
of the atmosphere, so as to form part of the water which is exhaled
from the lungs. Again, the sulphur and phosphorus of the food
are converted, by oxygenation, into sulphuric and phosphoric acids;
in which process, heat must be generated. In the composition of
urea, moreover, oxygen is present in much larger proportion, than it
is in the proteine-compounds by the metamorphosis of which it is
formed ; so that in its production, too, caloric will be generated. In
fact it may be stated as a general truth, that the whole excess of the
oxygen absorbed over that which is contained in the carbonic acid
exhaled (§ 690), must be applied to purposes in the laboratory of
the system, in which caloric will be disengaged. Still, the amount
of carbonic acid exhaled must always be the measure of the chemical
processes, by which heat is generated in the body ; because it is
itself the result of the chief of these processes (the union of carbon
and oxygen), and because the surplus amount of oxygen which is
absorbed, and w^hich is applied to other purposes, entirely depends
upon it.

766. The power of maintaining a high independent temperature is
usually much less in young warm-blooded animals, than in adults.
There are considerable variations in this respect, however, amongst
different species ; for where the young animal is born in such an ad-
vanced condition, as to be thenceforth almost independent of parental
assistance, it is capable of maintaining its own temperature ; but
where it is born in such a state as to require to be supplied wdth
food by the parent for some time, it is also more or less dependent
upon the warmth imparted to it from the parental body. This is
peculiarly the case with the young of the Human species, which is

438 REGULATION OF HEAT IN MAN.

longer dependent upon parental aid, than that of any other animal.
In the case of children born very prematurely, the careful sustenance
of their heat is one of the points most to be attended to in rearing
them ; and even the most vigorous infants, born at the full time, are
far from being able to keep up their proper standard without assist-
ance, if exposed to a cool atmosphere. It has been ascertained that,
during the first month of infant life, the mortality in winter is nearly
double that of summer, — being 1*39 in January to 0-78 in July ; and
this striking difference cannot be attributed to any other cause, than
the injurious influence of external cold, which the calorifying powers
of the infant do not enable it to resist. As age advances, the power
of generating heat increases, and the body becomes much more inde-
pendent of external vicissitudes ; so that, in adult life, the winter
mortality is to that of summer, only as 1*05 to 0-91, or less than one-
sixth more. In advanced age, the calorifying power again diminishes ;
and this we should anticipate, from the general torpor of the nutritive
operations in old persons. Between 50 and 65 years of age, the re-
lative winter and summer mortality are nearly as in the first month of
infancy ; and at 90 years, the average mortality of winter is much
more than twice that of summer, being as 1*58 to 64.

767. It appears that there is not merely a difference in calorifying
power at different ages, but at different seasons ; the amount of heat
generated in summer not being sufficient, in many animals, to prevent
the body from being cooled down by prolonged exposure to a tempe-
rature, which is natural to them in winter. To what extent this is
the case with Man, it is difficult to say. His constitution is distin-
guished by its power of adapting itself to circumstances ; and he can
live under extremes of temperature more wide than those, which most
other animals can endure (§ 113). Whether in the torrid zone, or
in the arctic regions, he can maintain his healthy condition under
favourable circumstances; in each case his natural appetite leading
him to the use of that kind and amount of food, which are best suited
to the wants of his system. But the longer he has been habituated
to a very warm or a very cold climate, the more difficult he at first finds
it to live comfortably in one of an opposite character ; as his consti-
tution, having become adapted to one particular set of circumstances,
requires time to accommodate itself to an opposite one.

768. The means by which the heat of the body is prevented from
rising above its normal standard, even in the midst of a very high
temperature in the surrounding air, are of the most simple character.
The excreting action of the skin is directly stimulated by the applica-
tion of warmth to the surface; and the fluid which is poured forth,
being immediately vaporized, converts a large quantity of sensible
caloric into latent, and thus keeps down the temperature of the skin.
By this provision, the body may be exposed with impunity to dry air
of 600° or more, so long as the supply of fluid be maintained. But
it cannot long sustain exposure to air saturated with vapour, even

ANIMAL LUMINOSITY. 439

though it may not be many degrees hotter than the body ; because
the cooling act of evaporation from the skin cannot then be carried on.

769. The evolution of Light is a very interesting phenomenon,
chiefly witnessed among the lower Animals, and usually supposed not
to occur in any class above Fishes. It is particularly remarkable
among the Radiata and inferior Mollusca. A large proportion of the
Acalephce, or Jelly-fish tribe possess the property of luminousness in
a greater or less degree ; and it is to small animals of this class, which
sometimes multiply to an amazing extent, that the beautiful phenome-
non oi phosphorescence of the sea is chiefly due. In the midst of the soft
diflfused light thus occasioned, brilliant stars, ribbons, and globes of
fire are frequently seen ; these appearances being due to the lumino-
sity of the larger species of the same tribe, or to that of other marine
animals. — Some of the most remarkable examples of luminosity, in
regard to the brilliancy of the light emitted, occur in the class of
Insects. Here the emission is confined to one portion of the body,
or to two or more isolated spots, instead of being diffused over a larger
surface ; and it is proportionably increased in intensity.

770. The phenomenon of Animal Luminousness appears usually
attributable to the formation of a peculiar secretion ; which, in many
instances, continues to shine after removal from the Animal, so long
as it is exposed to the influence of oxygen : and it seems not unrea-
sonable to believe, that it depends upon a slow process of combustion,
analogous to that which takes place when phosphorus is exposed to
the air. There is a special provision, in Insects, for conveying a
large supply of air through the peculiar substance, which is deposited
beneath the luminous spots ; and the power which Glow-w^orms, Fire-
flies, &c., possess, of suddenly extinguishing their light, and as sud-
denly renewing it, seems to depend upon their control over the air-
aperture or spiracle by which air is admitted, — the stoppage of the
supply of air causing the immediate cessation of the luminousness,
and its re-admission occasioning a renewal of the process on which it
depends. — It is probable, however, that in certain cases, the lumino-
sity is rather of an electrical character. There are several of the smaller
Annelida or marine Worms, which are brilliantly luminous when irri-
tated ; the luminosity having the character, however, of a succession
of sparks, rather than of a steady glow. It appears from the recent
experiments of M. Quatrefages, that this peculiar luminosity is the
especial attribute of the muscular system ; and that it is produced w4th
every act of muscular contraction in these animals.

771. Although no such luminosity is commonly manifested in any
of the higher vertebrata, or in Man, yet there are well-authenticated
cases, in which the phenomenon has presented itself in the living sub-
ject,*— luminous emanations from dead animal matter being of no
unfrequent occurrence. In most of these cases, however, the indi-

* See an account of several cases of the Evolution of Light in the Living Human
Subject, by Sir Henry Marsh, M. D., M. R. L A., &,c.^

440 ANIMAL ELECTRICITY.— ELECTKIC FISHES.

viduals exhibiting the luminosity had suffered from consumption, or
some other wasting disease, and were near the close of their lives at
the time ; so that it is probable that a decomposition of the tissues was
actually in progress, analogous to that which, when it occurs after
death, imparts luminosity to the decaying body. One instance is
recorded in which a large cancerous sore of the breast emitted light
enough, to enable the hands on a watch-dial to be distinctly seen when
it was held within a few inches of the ulcer ; here, too, decomposition
was obviously going on, and the phosphorescent matter produced by
it was exposed to the oxygenating action of the atmosphere.

771. Slight manifestations of free Electricity ^ or, in other words,
disturbances of Electric equilibrium, are very frequent in living ani-
mals ; and they are readily accounted for, when we bear in mind that
nearly all chemical changes are attended with some alteration in the
electric state of the bodies concerned ; and when we consider the
number and variety of such changes in the living animal body.
When slight, however, they can only be detected by refined means
of observation; and it is only when they are considerable, that they
attract notice. The most remarkable examples of the evolution of
free Electricity in Animals, are to be found in certain species of the
class of Fishes ; the best known of which are the Torpedo or Elec-
tric Ray, and the Gymnotus or Electric Eel. These possess organs,
in which Electricity may be generated and accumulated in large quan-
tities, and from which it may be discharged at will. The shock of a
large and vigorous Gymnotus is sufficiently powerful to kill small
animals, and to paralyze large ones, such as men and horses : that of
the Torpedo is less severe, but it is sufficient to benumb the hand that
touches it.

772. The electric organs of the Torpedo (which, from being found
on European shores, has been the most studied) are of flattened shape,
and occupy the front and sides of the body ; forming two large masses,
which extend backwards and outwards from each side of the head.
They are composed of two layers of membrane separated by a con-
siderable space ; and this space is divided by vertical partitions into
hexagonal cells like those of a honeycomb, the ends of which are
directed towards the two surfaces of the body. These cells, which
are filled with a whitish soft pulp, somewhat resembling the substance
of the brain, but containing more water, are again subdivided hori-
zontally by membranous partitions; and all these partitions are pro-
fusely supplied with blood-vessels and nerves. — The electrical organs
of the Gymnotus are essentially the same in structure ; but they differ
in shape, in accordance with the conformation of the animal. — In
these, and the other Electrical fishes, the electric organs are supplied
with nerves of very great size, larger than any others in the same
animals, and larger than any nerves in other animals of similar bulk.
These nerves arise from the top of the spinal cord, and seem analo-
gous to the pneumogastrics of other animals.

773. The following conditions appear to be essential to the mani-

r

ELECTRIC FISHES. 441

festation of the Electric powers of these animals. Two parts of the
body must be touched at the same time ; and these two must be in
different electrical states. The most energetic discharge is procured
from the Torpedo, by touching its back and belly simultaneously; the
electricity of the back being positive, and that of the belly negative.
When two parts of the same surface, at an equal distance from the
electric organ are touched, no effect is produced, as they are equally
charged with the same electricity; but if one point be further from it
than the other, a discharge occurs, the intensity of which is propor-
tioned to the difference in the distance of the points from the electric
organ. However much a Torpedo is irritated, no discharge can take
place through a single point; but the fish makes an effort to bring the
border of the other surface in contact with the offending body, through
which a shock is then transmitted. This, indeed, is probably the usual
way in which the discharge is effected. — The identity of animal with
common Electricity is proved, not merely by the similarity of the
effects upon the feelings produced by the shock of both ; but also by
the fact that a spark may be obtained, and chemical decompositions
effected by the former, precisely as by the latter.

774. The voluntary power of the animal over its Electric organs, is
dependent upon their connection with the nervous centres. If all the
nerve-trunks supplying the organ on one side, be divided, the animal's
control over that organ will be destroyed ; but the power of the other
may remain uninjured. If the nerves be partially divided on either
or both sides, the power is retained by the portions of the organs,
which are still connected with the brain by the trunks that remain.
Even slices of the organ, entirely separated from the body except by a
nervous fibre, may exhibit electrical properties. Discharges may be
produced, by irritating the part of the nervous centres from which the
trunks proceed, so long as the latter are entire ; or by irritating the
portions of the divided trunks, which remain in connection with the
electric organs ; or even by irritating portions of the electric organs
themselves, when separated from the nervous centres. — In all these
respects, there is a strong analogy between the action of the nerves on
the Electric organs, and their action on the Muscles. And as the
latter contract by their own inherent powers, when stimulated by nerv-
ous influence, so does there seem reason to believe, that the evolution
of Electricity takes place from some peculiar changes in the electric
organs, of which changes the agency of the nerves is one of the con-
ditions. To the idea that the nervous centres produce the electricity,
that the nervous trunks convey it, and that the electric organs serve
merely to store it up, there are several objections, and especially
these ; — that there is nothing whatever in the structure of the brains
of the Electrical Fishes, that marks them out as essentially differ-
ent from those of the species to which they are otherwise allied ; —
that the power of the nerve-trunk, in conveying the requisite stimu-
lus to the electric organs, is destroyed as completely by tying, as by
dividing the trunk, which would not be the case if the nervous

442 MANIFESTATIONS OF ELECTRICITY.

agency were itself of the nature of ordinary electricity (§ 396); —
and that electric manifestations may be procured from the electric
organs, by stimuli applied to themselves, after the complete severance
of their connection with the brain, — ^just as muscles may be thrown
into contraction by direct stimulation, under the same circumstances
(§348).

775. It is another interesting point of analogy between the action
of Muscles, and that of the Electrical organs, that the former (as is
now fully proved by the elaborate and exact researches of Matteuci),
is attended with electrical disturbance. In any fresh vigorous mus-
cle, in a state of passive or tonic contraction, there is a continual
electric current from the interior to the exterior, sufficient to excite
the leg of a frog to energetic contraction, when its nerve is so ap-
plied to the muscle, as to receive the influence of this current. And
a much more powerful current is produced, when the muscle is thrown,
by a stimulus applied to its own nerve, into a state of energetic con-
traction. The explanation of the constant direction of the current,
from the interior towards the exterior of the muscle, seems to be, that
the changes connected with the nutrition and disintegration of the
muscular tissue go on more energetically in its interior, than they do
nearer its surface, where the proper muscular fibres are mingled with
a large proportion of areolar and tendinous substance.

776. It has also been shown that there exists in the Frog, during
its whole life, a continual current of Electricity, passing from its
extremities towards its head. The conditions on which this current
depends do not seem very evident; and as it has been detected in
no other animal, it has been termed the courant propre, or peculiar
current, of the Frog. It bears this curious analogy to the electric
discharges of Fishes; that it is not manifested, if the connection be
made between corresponding points of the opposite sides; but that it
shows itself, when the communication is made between points higher
or lower in the body, whether on the same or on opposite sides.

777. Manifestations of Electricity may be produced, in most animals
having a soft fur, by rubbing the surface, especially in dry weather ;
this is a fact sufficiently well known in regard to the domestic Cat.
Some individuals of the Human race exhibit spontaneous manifesta-
tions of electricity, which are occasionally of very remarkable power.
There are persons, for instance, who scarcely ever pull off articles of
dress, which have been worn next their skin, without sparks and a
crackling noise being produced, especially in dry weather. This is
partly due, however, to the friction of these materials with the surface,
and with each other. But the case of a lady has been recently put
on record, who was for many months in an electric state so different
from that of surrounding bodies, that, whenever she was but slightly
insulated by a carpet or other feebly-conducting medium, sparks
passed between her person and any object which she approached.
When she was most favourably circumstanced, four sparks per minute
would pass between her finger and the brass ball of a stove at a dis-

f I

REPRODUCTION. 443

tance of IJ inch. Various experiments were tried, with the view of
ascertaining if the Electricity was produced by the friction of articles
of dress ; but no change in these seemed to modify its intensity. From
the pain which accompanied the passage of the sparks, this condition
was a source of much discomfort to the subject of it.

CHAPTER XL

OF REPRODUCTION.

1 . General View of the J\*ature of the Process.

778. There is no one of the functions of living beings, that dis-
tinguishes them in a more striking and evident manner from the inert
bodies which surround them, than the process of Reproduction. By
this function, each race of Plants and Animals is perpetuated; whilst
the individuals composing it successively disappear from the surface
of the earth, by that death and decay which are the common lot of all.
There are certain tribes, in which the death of

the parent is necessary for the liberation of the ^'^- ^-^■

germs, from which a new race is to spring up.

This is the case, for example, in some of the

simplest Cellular Plants; in which every cell

lives for itself alone, and performs its w^hole

series of vital operations independently of the

rest; and in which the process of reproduction

consists in the rupture of the parent-cell, and the

emission of the contained reproductive particles,

every one of which is capable of developing simple isoiat<dceiiscon-

itself into a new cell, resembling that of its Ss".^ reproductive moie-

parent and capable of going through the same

series of changes (§ 31). But as, in more complex organisms, we

find certain cells set apart for Absorption, others for Secretion, &c.,

so do we find a particular group of cells set apart for Reproduction ;

and these go through a series of changes analogous to those juvSt

described, yet without interfering with the general life of the structure.

779. Among many of the lower Animals, a multiplication of indi-
viduals takes place by a process that closely resembles the budding of
Plants ; this must be regarded, however, not as a proper act of Repro-
duction, but as a modification of the ordinary Nutritive process. The
same may be said of the powers of reparation, which every Animal
body possesses in a greater or less degree, but which are by far the
most remarkable among the lower tribes ; for when an entire member
is renewed (as in the Star-fish), or even the whole body is regenerated

444 SIMPLEST FORMS OF REPRODUCTIVE PROCESS.

from a small fragment (which is the case in many Polypes), it is by a
process exactly analogous to that which is concerned in the repara-
tion of the simplest wound in our own bodies, and which, as already
explained (§ 636), is but a modification of the process that is con-
stantly renewing, more or less rapidly, every portion of their fabric.
The essential character of the special function of Reproduction, con-
sists in the entire separation of certain germs from the parent structure ;
which are capable, by their own inherent powers, of developing
themselves into new individuals: the only conditions requisite, being
a proper supply of nutriment, and a certain amount of warmth. In
the case of the simple Cellular Plants just now adverted to, the germs,
when set free from the parent-cell, are thrown at once upon their own
resources, and draw from the surrounding elements the materials of
their growth and development (§ 32). But in the higher Plants, we
find not only a set of germ-preparing organs, or reproductive cells
(the pollen-grains), but also a set of germ-nourishing organs (the
ovules); into which the reproductive granules are received, and in
which they are supplied with nutriment previously elaborated by the
parent, that serves to nourish them during the early stages of their
development.

780. This is the universal method in which the Reproductive pro-
cess is effected in Animals ; the concurrence of two sets of organs
being always necessary, — the germ-preparing organs, or seminal cells;
and the germ-nourishing organs, or ova. These may be united in the
same individual, as they are in most plants; and the ova may be fer-
tilized from the seminal cells of the same being; — as happens in some
of the lowest tribes of MoUusca. Or, the two sets of organs being
present in each individual, it may not be capable of self-impregnation;
but, in the congress of two individuals, each impregnates, and is im-
pregnated by the other ; — as may be observed in the Snail, and many
of the higher Mollusks. Or the sexes may be altogether distinct ;
one individual possessing only the male or germ-preparing organs ;
and the other the female, or germ-nourishing apparatus.

781. The early Development of Animals may be so much better
understood, when the general history of that of Plants is compre-
hended, that it is desirable here to give an outline of the latter sub-
ject.— Where, as in the simplest Cellular Plants, each individual
consists, even in its adult state, but of a single cell, the development
of one of the reproductive granules into the complete cell constitutes
the whole history of its growth. In other cases, however, w^e have
an extension of the original structure by a process of budding; so
that, from the first-formed cell, a cluster, or filament, may be pro-
duced, according to the mode in which this budding takes place.
Thus it may occur, as in Palmella, very much in the manner of or-
dinary Cartilage-cells, (§ 267, Fig. 37,) so as to produce a cluster of
2, 4, 8 or more ; or it may proceed in a linear direction, as in Carti-
lage-cells near the ossifying surface, (Fig. 48,) so that a filament is the
result, as the ordinary ConfervcB. Now if the cells of one of the sim-

REPRODUCTIVE PROCESS IN PLANTS. 445

pie Confervse, which is composed of single rows, bud out laterally, as
well as longitudinally, a leaf-like expansion is formed, like that of
the Sea-weeds. This simple organ has the power of performing the
functions of absorption, digestion, respiration, &c., as well as that of
reproduction ; and as it differs from the leaves of the higher plants
(to which it otherwise bears a close resemblance), in its power of per-
forming the last-named function, it is distinguished by the name of
frond.

782. Although, in the highest Cryptogamia, the character of the
Plant is ultimately to become very different from this, its formation
commences in precisely the same manner; so that the young Fern,
which is afterwards to send a w^oody stem and beautifully-formed
leaves into the air, and to transmit its solid roots deep into the ground,
might be readily mistaken for an humble Liverwort, whose frond is
not destined to raise itself from the ground, but creeps along its sur-
face, and obtains its nourishment by the slight fibres which insinuate
themselves into the soil. In both cases, the primary frond is evolved,
in a precisely similar manner, by the budding of the original cell;
but the Liverwort remains upon the lower grade, beyond which it is
never destined to pass, — the primary frond being, in that class, the
permanent plant ; w^hilst in the Fern, the primary frond is a tempo-
rary organ merely, the purpose of which is to obtain and elaborate
the nutriment, that is destined for the evolution of the permanent
structure. It is from the centre of this leafy expansion, that the true
stem and roots of the Fern are subsequently put forth ; and the whole
of the primary frond decays away, as soon as the first true leaf has
unfolded itself.

783. Although the embryo of the Flowering Plant is developed
under different conditions, — that is, at the expense of the nutriment
provided for it in the seed, within which it is contained, — yet the
history of its growth is essentially the same. The mass of cells, which
originates from the pollen-granules that fertilize the ovule, does not
at first take the form which the young plant is afterwards to present ;
but spreads itself out into a single or double cotyledon^ which is a
leaf-like expansion, closely resembling the primary frond of the Fern.
It is by this organ, that the nourishment provided in the ovule is ab-
sorbed and prepared for the development of the young plant ; the
permanent fabric of which, even when the seed is mature, forms but
a very small proportion of it. The development of the permanent
structure takes place rapidly, however, during the process of germi-
nation; in which all the nourishment contained in the seed is pre-
pared for the embryo by the cotyledons ; these serving the purpose of
leaves, until the stem and roots have been developed, and the true
leaves unfolded. By the time that this store has been exhausted, the
development of the embryo has advanced sufficiently far, to enable it
to support itself; and the cotyledons then decay away.

784. Thus we see that even the highest Plants have to pass through
the conditions, which are permanently shown in the lower; and that

446

REPRODUCTION IN ANIMALS.— ACTION OF MALE.

the parts which are first formed, are destined for a temporary purpose
only. We shall find, in tracing the history of the development of
Animals, that exactly the same general fact may be observed, in even
a higher degree; — the number of different stages being greater; and
an even larger proportion of the parts first formed, in the embryo of
the higher tribes, having a merely temporary purpose, and being
destined to an early decay, as soon as the more permanent portions of
the fabric have been evolved.

Fig. 129.

2. Jiction of the Male,

785. The share in the Reproductive function, which belongs to
the Male Sex, essentially consists in the formation and liberation of
the reproductive particles. These are prepared within peculiar cells,

as already described (§ 240) ; and the
cells are either scattered through the
soft parenchyma of the body, as hap-
pens among some of the lowest ani-
mals ; or they are confined to certain
parts of it, as in those a little more
elevated in the scale ; or they are
formed within follicles or tubes, clus-
tered together into an organ of a gland-
ular character, known as the Testis.
Such an organ is found in all Insects
and Mollusca ; as well as in Verte-
brated Animals. In the first of these
classes, it is formed on the general
plan of their proper glands (§ 720);
being usually composed of tubes, more
or less elongated, and sometimes ter-
In the Mollusks, on the other hand,
it is almost invariably composed of clusters of follicles. In either
case, the seminal cells are developed within the tubes or follicles, as
are the ordinary secreting cells of the Liver or Kidney within the
tubes or follicles of those glands ; and their contents are discharged
by an excretory duct, which terminates in an organ that conveys them
out of the body, either emitting them into the surrounding water (as
happens with many Mollusca), or depositing them within the body of
the female. It is curious that, in some of the lowest Fishes, we should
return to one of the simplest conditions of this organ, — a mass of vesi-
cles, without an excretory duct. In these cases, the secretion formed
within the vesicles escapes, by their rupture, into the abdominal
cavity ; whence it passes out by openings that lead directly to the
exterior.

786. The Testis in Man is formed, in every essential particular,
upon the plan of the ordinary Glands. It consists of several distinct
lobules, separated by processes of the fibrous envelop, or tunica

Formation of Spermatozoa within semi-
nal cells :— a, ihe original nucleated cell;
b. the same enlarged, with the formation of
the Spermatozoa in progress ; c. the Sper-
matozoa nearly complete, but still enclosed
within the cell.

minating in enlarged follicles.

STRUCTURE OF THE TESTIS.

447

Fig. 130.

albuo^inea, which pass down between them ; and each lobule consists
of a mass of convoluted tubuli seminiferi, through which blood-ves-
sels are minutely distributed. The
diameter of these tubuli is tolerably uni-
form ; being, when thev are not over-
distended, from l-195th to 1- 170th of
an inch. They form frequent anasto-
moses with each other ; and on this
account it is difficult to trace out their
free or caecal extremities. The tubuli
of each testis discharge their contents
into an efferent duct, the Vas-deferens;
and by this the product is conveyed
into the Vesicula seminalis on each
side, which, like the gall-bladder and
Urinary bladder, serves to store up the
secretion until the proper time for dis-
charging it. The product of the action
of the Testis consists of a fluid, through
which the Spermatozoa are diffused, —
these last bodies being usually set free
by the rupture of the seminal cells be-
fore they leave the tubuli of the testis.
It is difficult to determine the precise
characters of the fluid portion of the
secretion ; as this is mingled with other
secretions (such as that of the Prostate
gland, and of the mucous lining of
the Vesiculse seminales and spermatic
ducts) before it is emitted. And an exact analysis is not of much
consequence ; since there can be no doubt that the peculiar powers
of the fluid depend upon the Spermatozoa. It may be stated, how-
ever, that the Spermatic fluid has an alkaline reaction, and that it
contains albumen, together with a peculiar animal principle termed
Spermatine ; and that it also includes saline matter, consisting chiefly
of the muriates and phosphates, especially the latter, which form crys-
tals when the fluid has stood for some little time.

787. The minute filamentous bodies set free by the rupture of the
spermatic cells, are distinguished by their power of spontaneous move-
ment, which occasioned them to be long regarded as proper Animal-
cules. It is now clear, however, from the history of their develop-
ment, as well as from other considerations, that they cannot be justly
regarded in this light; and that they are analogous to the reproductive
particles of Plants, which, in many cases, exhibit a spontaneous mo-
tion of extraordinary activity, after they have been set free from the
parent structure. The human Spermatozoon consists of a little oval
flattened body, from the l-600th to the l-800th of a line in length;
from which proceeds a filiform tail gradually tapering to a very fine

Anatomy of the Testis : — 1, 1, The tu-
nica albuginea. 2, 2. The mediastinum
testis. 3, 3. The lobuli testis. 4, 4. The
vasa recta. 5. The rete testis. 6. The
vasa efferentia, of which six only are
represented in this diagram. 7. The coni
vasculosi, constituting the globus major of
the epididymis. 8. The body of the epi-
didymis. 9. The globus minor of the
epididymis. 10. The vas deferens. 11.
The vasculum aberrans.

448 FORMATION OP SEMINAL SECRETION.

point, of l-50th or at most l-40th of a line in length. The whole is
perfectly transparent ; and nothing that can be called structure can be
satisfactorily distinguished within it. The movements are principally
excited by the undulations of the tail ; which give a propulsive action
to the body. They may continue for many hours after the emission
of the fluid; and they are not checked by its admixture with other
secretions, such as the urine and the prostatic fluid. When the semi-
nal fluid remains in contact with a living surface (as when deposited
in the generative organs of the female) the Spermatozoa may retain
their vitality for some days ; and an instance has already been referred
to (§ 240), in which the later stages of the development of the Sper-
matozoa actually take place in this situation, — the seminal fluid
emitted by the male (among many Crustacea) not containing any
Spermatozoa completely formed, but numerous spermatic cells, which
undergo the remainder of their development, and then rupture and
set free their contents, within the oviducts of the female.

788. The power of procreation does not exist in the Human Male
(except in rare cases) until the age of from 14 to 16 years; at which
epoch, the sexual organs undergo a much increased development ; and
the instinctive desire, which leads to the use of them, is awakened in
the mind. From that time, to an advanced age, the procreative power
remains, in the healthy state of the system ; unless it be exhausted by
excessive use of it, or by too energetic a direction of the mental or
corporeal powers to some other object. The formation of Seminal
fluid being, like the proper acts of Secretion, very much influenced by
conditions of the nervous system, is increased by the continual direc-
tion of the mind towards objects which arouse the sexual propensity;
and thus, if sexual intercourse be very frequent, a much larger quan-
tity of the fluid will be produced, than if it is more rarely emitted,
although the amount discharged on each occasion will be less. The
formation of this product is evidently a great tax upon the corporeal
powers; and it is a well-known fact, that the highest degree of bodily
and mental vigour is inconsistent with more than a very moderate
indulgence in sexual intercourse ; whilst nothing is more certain to
reduce the powers, both of body and mind, than excess in this respect.

789. It may be stated as a general law, prevailing equally in the
Vegetable and Animal kingdoms, — that the development of the indi-
vidual, and the reproduction of the species, stand in an inverse ratio
to each other. We have seen that, in many organized beings, the
death of the parent is necessary to the production of a new generation ;
and even in numerous species of Insects, it follows very speedily upon
the sexual intercourse. It is a curious fact, that Insects which usu-
ally die, the male almost immediately after the act of copulation,
and the female very soon after the deposition of the eggs, may be
kept alive for many weeks or even months, by simply preventing
their copulation. And there can be no doubt, that, in the Human
race, early death is by no means an unfrequent result of the excessive
or premature employment of the genital organs ; and where this does

DEPENDENCE OF ANIMAL EMBRYO ON FEMALE PARENT. 449

not produce an immediately fatal result, it lays the foundation of future
debility, that contributes to produce any forms of disease to which
there may be a constitutional predisposition, especially those of a
Scrofulous nature.

790. The emission of the Spermatic fluid is an act of a purely refiex
nature; the Will having no power either to efTect or to restrain it.
The stimulus is given by the friction of the surface of the Glans Penis
against the rugous walls of the Vagina; the sensibility of the organ
being at the same time much increased, by the determination of blood
to it. The impression is at last sufficiently strong to produce, through
the medium of the lower part of the Spinal cord, (which is the gangli-
onic centre of the circle of afferent and efferent nerves connected with
this organ,) a reflex contraction of the muscles surrounding the vesi-
culse seminales. These receptacles discharge their contents (which
consist partly of the Spermatic fluid, and partly of a secretion of their
own), into the Urethra ; and from this they are expelled with some
degree of force and with a kind of spasmodic action, by its own
Compressor muscles. Although the sensations concerned in this act
are ordinarily most acutely pleasurable, yet there appears to be suffi-
cient evidence that they are by no means essential to its performance;
and that the impression conveyed to the Spinal cord may excite the
contraction of the Ejaculator muscles, like other reflex operations,,
without producing sensation (§ 394).

3. Action of the Female.

791. As it is the office of the Male to prepare the germ of the
future being, and then to set it free, so is it the part of the Female to
receive this germ, and to supply it with the materials for its develop-
ment, up to the condition in w^hich it can support its own life. The
mode in which this is accomplished, is essentially the same with that,
in which the process is effected in Plants. In certain parts of the
female structure are developed peculiar bodies termed oi;a; which,
contain a store of nutriment, adapted to supply the wants of the germ.
The reproductive particles find their way into these, and begin to-
grow at the expense of the materials which they meet with in their
interior. This may enable the embryo to develop itself, without any
further assistance (save a warm temperature), into the form it is per-
manently to assume ; as in the case of Birds and Reptiles, which do'
not come forth from the investments of the e^^^ until they have at-
tained the form characteristic of the group to which they belong. Or
it may only serve for the early part of the process ; and one of two
methods may then be employed to complete it. Either a new con-
nection is formed between the parent and embryo, by which the
former continues to supply the latter with nutriment, more directly
from its blood ; as is the rase with Mammalia — or the embryo issues
from the egg, in a condition very unlike that which it is permanently
to attain, but in a form which enables it to acquire its own nourish-

29

450 DEVELOPMENT OF OVA IN OVARIUM.

ment, and to pass through the latter stages of its evolution quite inde-
pendently of any assistance from its parent ; this is the case with a
large proportion of the Invertebrata.

792. Sometimes the permanent form of the latter is elaborated, as
it were, out of the temporary, by the gradual development of new
parts ; as happens in most of the Worm tribe, — the animal, at the
time of its first emersion from the egg, possessing but a few segments,
or even but a single one ; but afterwards, by the progressive develop-
ment of new segments, to the number in some instances of several
hundreds, acquiring a great length. In other cases, there is a com-
plete metamorphosis or change of form ; the animal at its emersion
from the egg, not merely having an aspect which is entirely different
from that which it is ultimately to present, but possessing organs
which it is afterwards to lose. Thus the Frog emerges in the state of
a Fish ; and in this, its Tadpole condition, it breathes by gills, swims
by its tail, and has all the essential characters of the class below its
own. Certain of its organs gradually disappear altogether, whilst
others are as gradually developed; and in this manner the temporary
Fish is converted into the permanent Reptile. The metamorphosis is
even more striking in Insects ; which come forth from the egg as
"Worms ; and which attain their complete form by what appears to be
a sudden change, — this change being really, however, of a very gra-
dual character, the organs characteristic of the perfect Insect being
slowly developed, during the preceding state of quiescence which
usually characterizes the life of the Chrysalis, but being displayed
and brought into use only when the Chrysalis-skin is thrown off.
Thus the whole life of the Insect, up to this last change, may be re-
garded as one of embryonic development ; and the same may be said
of the condition of the Frog, up to the time w^hen its permanent
organs are fully evolved.

793. The Ova, like the seminal cells, are scattered through the soft
parenchyma of the body, in animals of the lowest class; but they are
more commonly developed in certain distinct portions of the fabric ;
being sometimes formed in the midst of solid masses of areolar or
cellular texture ; whilst in other instances they are developed, like
the spermatic cells, in the interior of tubes and vesicles resembling
those of glands, and furnished with an excretory duct. The latter
condition obtains in the greater proportion of the higher In vertebrated
animals, and in some Fishes ; but in the Vertebrated classes we return
to the type w^hich characterizes the egg-producing organs in many
Zoophytes, — namely, the development of the egg in the midst of a
mass of solid parenchyma, from which it gradually makes its way, to
escape into the abdominal cavity. The Ovarium of the Mammal,
Bird or Reptile, as well as that of most Fishes, differs entirely, there-
fore, from that of the Invertebrata ; for the latter have all the essen-
tial characters of true glands ; whilst the former are nothing else than
masses of parenchyma, copiously supplied with blood-vessels, and
having dispersed through their substance certain peculiar cells, termed

STRUCTURE AND DEVELOPMENT OF OVUM. 451

ovisacs^ within which the ova are developed. In order that the latter
may be set free, not only must the ovisac itself burst (like parent-cells
in general), but the peculiar tissue, and the envelops, of the ovarium
must likewise give way. When the ova thus escape into the ab-
dominal cavity, they may lie there for some time, at last to be dis-
charged through simple openings in its walls, as happens in those
Fishes which have this form of ovarium ; or they may be at once
received into the trumpet-shaped expansions of tubes, that shall con-
vey them to these orifices. These tubes are termed oviducts, in com-
mon with the excretory ducts of the glandular ovaria of Invertebrated.
animals ; for their function is the same, — that of conveying the ova
to the outlet by which they are extruded from the body. They are
represented in Mammalia by the Fallopian tubes, which are true ovi-
ducts ; but these unite and enlarge to form a Uterine cavity, in which
the embryo may be retained, whilst it is receiving the further assist-
ance to its development, in the manner to be presently explained.
This uterine cavity is peculiar to the Mammalia ; but there are many
cases among the lower classes, in which the ovum is retained within
the oviduct, so that the young comes into the world alive ; and a few
in which, during this delay, it receives a direct supply of additional
nourishment from the fluids of its parent.

794. The essential structure of the ovule, or unfertilized egg, ap-
pears to be the same in all animals. It consists externally of a mem-
branous sac, termed, from the nature of its contents, the yelk-bag.
The yelky or contained fluid, consists chiefly of albumen and oil-
globules ; and it is this substance, which, like the starchy and oily
matter laid up in the seed of the Plant, is destined to afford support
to the embryo, until it is able to obtain its own nutriment, or, as in
Mammalia, forms a new connection with the parent. Floating in
this fluid is a cell of peculiar aspect, termed the germinal vesicle ; and
upon its wall is a very distinct nucleus, termed the germinal spot. —
The layer of albumen surrounding the yelk, and termed the white of
the Bird's egg, together with the membrane which envelops this and
forms the basis of the shell, are not added until after the ovum has
left the ovarium. They are not present in the eggs of many of the
lower Invertebrata ; these consisting merely of the parts which are
formed within the ovarium.

795. The structure of the ovule in Mammals differs in no essential
particular from that just described ; but the yolk is much less in
amount, than in the ovules of Invertebrated animals ; since only the
very earliest stages of the development of the embryo are to take
place at its expense. We shall find that the ovule, after leaving the
ovarium and receiving the fertilizing influence, becomes enclosed,
whilst passing through the Fallopian tube, with a layer of albumi-
nous matter, which represents the white of the Bird's egg; and with
an additional fibrous envelop, which corresponds with the membrane
enveloping the latter. This fibrous membrane, termed the Chorion,
afterwards becomes subservient, however, to various important

452 PUBERTY.— MENSTRUAL DISCHARGE.

changes ; by means of which the ovum is again brought into con-
nection with the parent, to derive from the blood of the latter the
materials requisite for the continued development of the embryo.
These changes will be described hereafter (§ 811).

796. The Ovisac of Mammalia forms the inner layer of what is
termed the Graafian follicle^ after the name of its discoverer ; and
instead of closely enveloping the ovulum, as it does in oviparous
animals, it contains, in addition to it, a quantity of granular matter,
consisting of cells arranged in membranous layers, together with fluid.
Of these layers, one surrounds the ovulum, and is termed the tunica
granulosa; another lines the ovisac, and is named the memhrana
granulosa; whilst, to certain bands passing from the former to the
latter, and suspending the ovule (as it were) in the cavity of the
ovisac, the name of retinacula h^s been given by their discoverer,
Dr. Barry. — The outer layer of the Graafian follicle is formed by a
thickening and condensation of the surrounding parenchyma. of the
ovarium ; and it is quite distinct from the ovisac which it envelops.
It is extremely vascular, and is evidently destined to afford to the
structures within the materials for their development, which they re-
ceive and appropriate by their own powers of absorption and assimi-
lation.

797. The Mammalian Ovarium may be seen, even in the foetal
animal, to contain immature ova, enclosed within their ovisacs; and
the several parts of the former may be clearly distinguished, in those
which are in the more advanced stages of development. It appears
that, during the period of childhood, there is a continual rupture of
the ovisacs (or parent-cells), and a discharge of ova, at the surface of
the ovarium ; but these ova never attain so high a degree of develop-
ment, as to render them fit for impregnation. Their evolution takes
place more completely, as well as more rapidly, at the period of
puberty, when there is a greatly increased determination of blood to
the genital organs, and a correspondingly augmented energy in their
nutritive operations. At this epoch, the parenchyma of the ovarium
is crowded with ovisacs ; which are still so minute, that in the Ox,
according to Dr. Barry's computation, a cubic inch would contain
200 millions of them. Some of those nearest the surface, however,
are continually attaining increased development; and a rupture of
some of the Graafian follicles, and a discharge of ova prepared for
impregnation, from the exterior of the ovarium, thenceforth take
place, with more or less tendency to periodicity, during the whole
time that the female is in a state of aptitude for procreation.

798. In the Human female, the period of Puberty usually occurs
between the 13th and 16th year. The dififerences in the time of its
advent partly depend upon individual constitution, and partly upon
various external circumstances, such as temperature, habits of life, &c.
As a general rule, habitual exposure to a warm atmosphere, an inert
life, sensual indulgence, and circumstances that excite the sexual
feelings, favour the approach of Puberty ; whilst a cold climate and

^

MENSTRUAL DISCHARGE.— MATURATION OF OVA. 453

hardy life retard it. The appearance of the Catamenial discharge
usually takes place whilst the evolution of the genital organs is in
progress ; and it is a decided indication, when it occurs, that the
aptitude for procreation has been attained. It is not unfrequently
delayed much longer, however; and its absence is by no means to be
regarded as a proof of inability to conceive. The Catamenial secre-
tion, which proceeds from the lining membrane of the Uterus, seems
to consist of the elements of Blood, in an altered condition. It con-
tains a considerable amount of red colouring matter ; but the albu-
minous and fibrinous constituents seem to be present in smaller
proportion than in Blood. The coagulating power is for the most
part wanting, when the function is performed in a healthy manner ;
the appearance of clots being an indication that blood is escaping
from the secreting surface. The coagulation of the fibrin normally
present in the secretion, appears to be prevented by admixture with
the vaginal mucus ; but when an increased amount is poured forth,
this admixture is not sufficient to destroy its power of forming a clot.
In some cases of difficult Menstruation, which seem to depend upon
a state of low inflammation in the Uterus, the fibrin has such a tend-
ency to become organized, as to form shreds, or layers of false
membrane, which sometimes plug up the os uteri. The healthy
Menstrual secretion is remarkable for its very acid character.

799. This flux of altered blood from the lining membrane of the
Uterus, is not confined to the Human female, as was formerly sup-
posed ; but occurs in most of the lower Mammalia in the state of
heat^ or periodical aptitude for procreation, at which time the ova-
rium contains ova ready for impregnation. The chief peculiarity
attending its appearance in the Human female, is its regular monthly
return. In the natural condition of many of the lower Mammalia, as
in Oviparous animals, the period of heat recurs ai some one time of
the year, — usually in the spring ; or, in the smaller and more prolific
species, from two to six times. And in those which have undergone
a change by domestication, the recurrence is usually irregular, de-
pending upon various circumstances of regimen, temperature, &c.
The general analogy between the Menstruation of the Human female
and the heat of the lower Mammalia, — consisting in the peculiar apti-
tude for impregnation which then exists, in consequence of the matu-
ration of ova in the ovarium, — cannot now be questioned ; but it
appears that, in the Human female, ova may be matured and impreg-
nated at any part of the period, which elapses between the occur-
rences of the Catamenial discharge ; though it is certain that the apti-
tude for conception is much greater, during the few days which
precede and follow the menstrual period, than at any intervening
time. The duration of the period of aptitude for procreation, which
is marked by the continued appearance of the Catamenia, is more
limited in Women than in Men ; usually terminating at about the
45th year. It is sometimes prolonged, however, for ten or even fif-
teen years longer ; but cases are rare, in which women above 50

454 MATURATION OF OVA.

years of age have borne children. There is usually no menstrual
flow during pregnancy and lactation ; in fact, the cessation of the
Catamenia is usually one of the first signs indicating that conception
has taken place. It is by no means uncommon, however, for them
to appear once or twice subsequently to Conception ; and their ap-
pearance during Lactation, especially if it be much prolonged, is still
more frequent; hence it might be inferred, that the continuance of
Lactation would not prevent a fresh conception, — which is found to
be true in practice.

800. We shall now take a brief survey of the changes which occur
in the Ovulum, when it is being prepared for fecundation ; and of the
principal features of its subsequent development. — Up to the period
when the Ovule is nearly brought to maturity, it remains suspended
in the centre of the cavity of the Ovisac ; but it then begins to move
towards that side of the Graafian follicle, which is nearest the surface
of the ovarium. An important change is at the same time occurring
in the Graafian follicle itself; for whilst the part with which the ovule
comes in contact gradually thins away, the outer or vascular layer of
the remainder, especially on that side most deeply imbedded in the
ovary, becomes much increased in thickness ; and a deposition of
fibrinous matter seems to take place at that part, between this layer
and the inner layer or proper ovisac. This fibrinous matter is destined
subsequently to become more or less completely organized ; receiv-
ing vessels, which are prolonged into it from its enveloping mem-
brane: and it then forms the corpus luteum. The escape of the ovule
from the ovarium involves processes which are essentially the same,
whether it be impregnated or not ; but the subsequent changes difTer
in the two cases, so that the corpus luteum which accompanies the
pregnant state is a much more highly organized body than that which
is found in the ovary of the unimpregnated female. This difference
may be due in part to the absence, in the latter case, of that special
determination of blood to the genital organs, which takes place in the
former.

801. When the ovule is being thus brought near the surface of the
Ovary, a series of remarkable changes takes place in its interior.
The yelk becomes filled with cells; which, after passing through
several .generations (during which the transparency of the yelk is
much interfered with), completely disappear, leaving the fluid appa-
rently in the same condition as before. This process of cell-develop-
ment in the substance of the yelk, continues for some time after
fecundation ; and it probably has for its purpose, to prepare the mat-
ter of the yelk for its subsequent functions ; just as we have seen
reason to believe, that the albuminous matter of the chyle is ren-
dered fit for the nutrition of the body, by the development of floating
cells in its current (§ 213). But the most curious changes are those,
which take place within the germinal vesicle. Though previously
in the centre of the yelk, it now moves up towards one side of it,
and becomes flattened against the yelk-bag. At the same time, the

FERTILIZATION OF OVA. 455

edge of its nucleus begins to resolve itself into a ring of cells; which
sprout forth, as it were, from its inner wall, into its cavity. These
cells enlarge ; and another ring is developed nearer the centre of the
nucleus, pushing the former one outwards. A third ring is next
formed internally to the second ; and a similar development of suc-
cessive annuli of minute cells, one within another, continues, until
the whole germinal vesicle is filled with minute cells ; of which those
constituting the outer and first formed rings are the largest, whilst
those forming the central rings are very minute. The centre of what
was the germinal spot remains transparent ; and into this the germ
finds its way in the act of fertilization, by the means to be presently
described. All these cells, like those of the yelk, have a merely
temporary existence, and speedily deliquesce again ; and their func-
tion appears to be, to prepare the contents of the germinal vesicle for
being applied to the nutrition of the germ, which is to be subsequently
introduced into it.

802. By the changes in the position of the Ovulum and of its con-
tained parts, which have been already noticed, the germinal vesicle
is brought into very close proximity with the surface of the Ovary.
It is still covered, however, by the peritoneal coat of the ovary; by a
thin layer of the fibrous substance of that organ ; by the ovisac ; and
by the yelk-bag, which, in the Mammalian ovum, is known as the
zona pellucida. The three former of these envelops gradually thin
away, and at last rupture, and give passage to the ovule; which thus
escapes from the surface of the ovarium. At about the same time, a
chink or fissure is formed in the part of the yelk-bag, that covers the
central pellucid space of the germinal spot ; and into this space the
fertilizing influence appears to be introduced ; for we find it afterwards
occupied by two new cells, of very diflf'erent appearance from the rest,
from which the whole of the embryonic structure is subsequently to
be developed.

803. Much discussion has taken place, with regard to the exact
point at which the fertilization of the ovulum takes place ; but this does
not seem to be a matter of much consequence, as we find the order of
the diflferent steps to vary considerably in diflferent classes of animals.
Thus in many aquatic Mollusca, and even in a large proportion of
the class of Fishes, there is no act of copulation whatever ; but the
spermatic fluid, when emitted by the male, is diflfused through the
water, and fertilizes the ova, which have been deposited by the
female in his neighbourhood. In the Frog, again, and in other Rep-
tiles, the spermatic fluid is emitted upon the ova, at the time that they
are being extruded by the female. In many Insects and Crustacea, —
in which a single congress often serves to fertilize many thousand
eggs, the deposition of which occupies a period of several weeks or
months, — the spermatic fluid is received and stored up in a saccular
dilatation of the oviduct of the female, which is termed the spermo-
theca ; and in this manner it serves to impregnate the ova, as they are
successively developed, and are conveyed to the outlet of the oviduct.

456 EARLY CHANGES IN FERTILIZED OVUM.

In Birds, we find that ova are often set free from the ovarium in a
state of full maturity, but without fertilization ; and that they receive
their additional layer of albumen and their shelly envelop, in passing
down the oviduct, so as, at the time of their deposition, to differ in
no obvious particular from fertile eggs. It is doubtful, in regard to
Mammalia, whether the act of fertilization takes place before the ovum
has been actually discharged from the ovisac, or subsequently to its
finally quitting the ovarium and being received into the Fallopian
tube. It is quite certain that the spermatozoa frequently, if not inva-
riably, find their way to the surface of the ovary, being carried thither
by their own spontaneous movements ; and it seems on the whole
most probable, that the fertilization of the ova usually takes place
before they have been discharged from the ovisac, or whilst they are
still in the commencement of the Fallopian tube. It is not unlikely
that the place of the act of fecundation varies, according to the point
at which the ovule and the seminal fluid first come into contact, —
which may depend upon the degree of maturity of the ova at the
period of copulation.

804. Everything indicates that the contact of the Spermatozoon
with the Ovulum is the one thing needful in the act of fecundation ;
and there is strong reason to believe, that the large end of the Sper-
matozoon finds its way into the fissure just described, which is formed
in the Zona pellucida ; and that it there deposits the germs of the two
new cells, which are afterwards seen within the germinal vesicle.
We have seen that this is the essential nature of the fecundating pro-
cess in the Flowering Plant ; the reproductive granules, prepared
within the pollen-cell, being conveyed by the pollen-tube within the
ovule, where they speedily develop themselves into the first cells of
the embryonic structure. The manner in which the reproductive
germs of the Animal find their way to the ovary, is different, as we
have seen ; a power of spontaneous movement (which finds its resem-
blance in that of the sporules of the Confervae, &c.) being imparted
to them, by which they bring themselves into contact with the ovum.

805. From this stage, an entirely new set of changes begins to take
place in the interior of the Ovum, during its passage along the Fallo-
pian tube or oviduct. The two new cells, which at first occupy only
the pellucid centre of the germinal spot, rapidly increase in size, and
begin to develop new cells in their own interior. At the same time
they press upon the cells, which filled the germinal vesicle previously
to its fertilization; and these gradually liquefy or dissolve away, until
all trace of them is lost; and the twin-cells, with their offspring, are
alone contained within the germinal vesicle. Each of the first-formed
cells gives birth, by the usual process of cell-development, to a new
generation of two ; so that the number is now four; from these four
is produced a third generation of eight; and these go on progressively
doubling, until at last a mass is produced, closely resembling a mul-
berry, in which the number of cells is too great to admit of being
counted. This " mulberry mass" is obviously analogous to the col-

GERMINAL MEMBRANE.— CICATRICULA. 457

lection of cells, which is first developed within the seed of the Flower-
ing Plant (§ 783); and between the condition of the Animal and that
of the Vegetable embryo, at this period, there would not seem to be
any essential difference.

806. In the next stage, however, a marked

difference shows itself, which is very charac- Fig.isi.

teristic of the two kingdoms respectively. The
mass of cells, which is the rudiment of the
Vegetable embryo, spreads itself out into a flat
leaf-like expansion, — the primary frond, or co-
tyledon,— which remains as the permanent
form of the lowest plants, but is only tempo-
rary in the higher (§ 782). But in the embryo
of the Animal, the '' mulberry mass," having
moved up to the side of the yelk, and having Plan of early uterine ovum.

1 n ., 1 ■ . ', 1 • Within the external ring, or

become flattened against its enveloping mem- zona peiiucida, are the serous
brane, sends off from its edges a layer of cells, IrSpiem^e'rnb^r'yo; c.' "'^
which passes round the yelk, so as completely

to enclose it within a membranous envelop, the exterior of which is in
contact with the yelk-bag. A second layer is afterwards formed
within the preceding, from the central part of the mulberry mass ; and,
in the higher animals, a third is subsequently formed between them.
This membranous formation, as a whole, is known as the germinal
membrane ; its external pellicle is termed the serous layer ; the internal
is termed the mucous layer ; and the intermediate one, which gives
origin to the first vessels of the embryonic structure, is termed the
vascular layer.

807. Thus the first development of the Animal embryo is into a
sac, enclosing the store of nutriment that has been prepared for it, —
in fact, a stomach ; and we shall presently see, that it is by the agency
of the walls of this sac, that the nutrient materials which it encloses
are prepared for. being appropriated to the development of the more
permanent part of the fabric, which is to be evolved from the centre of
the mulberry mass. But we may here stop to notice the interesting
fact, that the development of the ovum in the /oz^es^ classes of animals
may be said almost to stop at this point ; the external layer of the
germinal membrane remaining as the integument ; the internal layer
becoming the lining of the stomach ; and the space occupied by the
yelk forming the digestive cavity, into which an entrance or mouth is
formed, by the thinning-away of the germinal membrane at a certain
point, round which tentacula or prolonged lips are usually developed.
This is the essential part of the history of development in the simpler
Polypes ; and we see how remarkably it corresponds with the history
of development of the lower Cryptogamic plants, in which the first-
formed membranous expansion, or primary frond, remains as the per-
manent leaf.

808. In the higher Animals, on the other hand, the greater part of
the germinal membrane, and of the cavity which it forms, have a

458 FORMATION OF CHORION.

merely temporary purpose ; being cast off, when they have performed
their function, like the cotyledons of Flowering Plants. Nearly the
whole of the permanent structure of the embryo is formed from a
single large cell; which at first occupies the centre of the "mulberry
mass ;" but which is seen at the surface of the latter, when this under-
goes the flattening already described. This cell, together with the
cluster of ordinary cells that surrounds it, is that which forms the
cicatricula or germ-spot upon the surface of the yelk-bag, in the im-
pregnated ovum of the Fowl; and, whilst still retaining its clearness,
it forms a large round transparent space in the centre of the cicatricula,
which is known as the Area pellucida. The nucleus of this Embryonic
cell, which was at first annular, changes its form into that of a pear,
and then into that of a violin ; and consists at last of two long parallel
lines, enclosing a narrow space between them, but separating and
enclosing a wider space at one extremity. In this state, it is called
the Primitive Trace. The same process then takes place within the
Embryonic cell, which has been described as occurring within the
Germinal vesicle ; the granules forming the outer border of the nucleus
being first developed into cells; these being pushed outwards by a
new series subsequently generated nearer the centre; and these being
displaced, in their turn, by a continuance of the same process. It is
from the peripheral cells originating in this primitive trace, that the
inner layers of the germinal membrane (§ 806) seem to be developed ;
the cells that originate nearer its centre, are those from which the
more permanent portions of the embryonic fabric are evolved. The
principal steps of that process will be presently noticed ; we must now
stop to consider the changes which take place in the female gene-
rative apparatus, subsequently to the liberation of the ovum from the
ovarium, but having relation to the new connection, which is to be
afterwards formed between the embryo and its parent.

809. During the time which is occupied by these important changes,
the Ovum passes through the Fallopian tubes, and makes its way into
the Uterus. During its transit through the Fallopian tubes, the Mam-
malium ovum, — like the ovum of Birds in its passage through the ovi-
duct,— receives an additional layer of albuminous matter secreted from
the walls of the tube ; and this is surrounded by a fibrous membrane,
whose structure and mode of formation have been described on a for-
mer occasion (§ 181). The outer layer of this envelop, in the egg of
the Bird, is further consolidated by the deposition of particles of car-
bonate of lime in its areolae ; but it undergoes no higher organization.
In the Mammal, however, this new envelop (termed the Chorion) is
a formation of great importance ; being the medium through which the
whole subsequent nutrition of the embryo is derived. This is at first
taken in by means of a number of villous processes, proceeding from
the entire surface of the Chorion, and giving it a spongy or shaggy
appearance ; these processes (which are composed of nucleated cells)
serve as absorbing radicles, which draw in the fluids afforded by the
parent ; and they thus make up for the early exhaustion of the small

FORMATION OF DECIDUA, AND VILLI OF CHORION. 459

supply of nutritious matter stored up in the ovum itself. The contained
embryo appropriates the fluid which is thus imbibed, by simple ab-
sorption through its surface; and thus it is nourished, until a more
special provision for its development comes into action. The struc-
ture of this organ, termed the Placenta^ cannot be understood, until
the concurrent changes in the lining membrane of the Uterus have
been considered.

810. This membrane, in its natural condition, presents on its free
surface the orifices of numerous cylindrical follicles ; which are ar-
ranged parallel to each other, and at right angles to the surface. In the
spaces between these follicles, the blood-vessels form a dense capillary
network. When impregnation takes place, this mucous membrane
swells and becomes lax ; its capillaries increase in size ; the follicles
are turgid with a white epithelium ; and the interfollicular spaces are
crowded with nucleated cells, which fill up the meshes of the capillary
network. In this peculiar condition, the uterine mucous membrane
is termed the Beddua. At a later period, the decidua may be found
to consist of two distinct layers ; the decidua vera^ lining the uterus ;
and the decidua reflexa, covering the exterior of the ovum. It was
formerly supposed that the latter was a portion of the former, which
had been pushed before the ovum at its entrance into the uterus; but
the two layers are now known to be so different in texture, that they
cannot be supposed to have the same origin ; and there seems much
probability in Mr. Goodsir's view, that the decidua vera is chiefly
formed by the highly vascular mucous membrane itself, and the deci-
dua reflexa by the abundant production of epithelial cells from its
follicles.

811. When the ovum has arrived in the Uterus, therefore, and the
villous tufts of its chorion are developed, these come into contact, in
the first instance, w^ith the layer of cellular decidua, which intervenes
between them and the vascular decidu?i. Through this cellular mem-
brane, therefore, the ovum must derive its nutriment from the vascular
surface ; and it cannot be deemed improbable, that the office of the
cellular decidua is to draw from the subjacent vessels the materials
which are to serve for the nutrition of the ovum, and to present it to
the villous tufts of the chorion. Each of these, as already mentioned,
is composed of an assemblage of nucleated cells, which are found in
various stages of development; and these are always enclosed within
a layer of basement-membrane, which seems itself to be composed of
flattened cells united by their edges. At the free extremity of each
villus, is a bulbous expansion, the cells composing which are arranged
round a central spot ; and it is at this point that the most active pro-
cesses of growth take place, the villus elongating by the development
of new cells from its germinal spot, and, like the spongiole of the
plant, drawing in nutriment from the soil in which it is imbedded. —
In its earliest grade of development, as already remarked, the chorion
and its villi contain no vessels ; and the fluid drawn in by the tufts is
communicated to the embryo, by the absorbing powers of its germinal

460 FORMATION OF VERTEBRAL COLUMN, AND OF VESSELS.

membrane. But when the tufts are penetrated by blood-vessels, and
their communication with the embryo becomes much more direct, the
means by which they communicate with the parent are found to be
essentially the same ; — namely, a double layer of cells, one layer
belonging to the foetal tuft, the other to the vascular maternal surface.
(See § 819.)

812. We now return to the Embryo itself; the general history of
whose development has been already traced, up to the period at which
the inner part of the elongated nucleus of the embryonic cell is begin-
ning to give origin to the permanent structures of the foetus. The
parts first formed in the embryo of Vertebrated animals, are such as
most characteristically distinguish them from all others ; — namely, the
Vertebral column, and Spinal Cord. The latter is formed in the
groove, which runs along the median line of the primitive trace ; and
it is surrounded, when first developed, by a tubular structure, which
has but a temporary existence in the higher Vertebrata, but which is
permanent in the lower Fishes. This structure, termed the Chorda
dorsalis, is found to be composed, wherever it exists, of nucleated
cells. From the cells exterior to this, the vertebral column is deve-
loped ; and this makes its first appearance in the condition of two
rows of minute opaque plates, imbedded in ridges that rise up on
either side of the central groove, and constituting the arches of the
incipient vertebrae. These ridges incline towards each other; and at
last meet and cover-in the groove, so as to complete the bony cylinder
protecting the spinal cord. Towards the anterior extremity, how-
ever, they do not at once close in ; and the large cells, in which the
great divisions of the Encephalon originate, may be seen between
them.

813. During the progress of
this change, another very im-
portant one is taking place, which
has reference to the nutrition of
the embryo during its further de-
velopment. This is the formation
of vessels in the substance of the
germinal membrane ; which ves-
sels serve to take up the nourish-
ment supplied by the yelk, as
well as that derived from the
chorion externally, and to con-
vey it through the tissues of the
embryo. These vessels are first
seen in that part of the vascular
lamina of the germinal mem-
brane, which immediately sur-
rounds the embryo ; and they
form a network, bounded by a
circular channel, which is known

Fig. 132.

Vascular Area of Fowl's egg, at the beginning of
the third day of incubation ;— a, a, yelk; 6, b, 6, b,
venous sinus bounding the area: c, aorta; d, punc-
tum saliens, or incipient heart; e, e, area pellucida;
/,/, arteries of the vascular area; §■,§•, veins; A, eye.

FORMATION OF VESSELS AND DIGESTIVE CAVITY. 461

under the name of the Vascular Area (Fig. 132). This gradually
extends itself, until the vessels spread over the whole of the germinal
membrane. The vessels are probably formed by the coalescence of
the original cells of the layer; and the first blood-discs which they
contain seem to originate in the nuclei of these cells. This network
of vessels serves to receive the nutritious matter contained in the
yelk-bag, and to convey it to the embryo ; but the act of absorption
seems to be performed here as elsewhere, by cells, — a layer of which
always intervenes between the vascular layer and the yelk itself.
These cells probably correspond in function with those of the villi of
the intestinal canal in the adult (§ 242); as the vessels of the yelk-
bag, or temporary digestive cavity, represent those of the alimentary
canal, to be afterwards developed from a portion of it. The vessels
of the yelk-bag terminate in two large trunks, which enter the embryo
at the point that afterwards becomes the umbilicus, and which are
known as the Omphalo- Mesenteric^ Meseraic, or Vitelline vessels. The
first movement of fluid takes place towards the embryo ; and this may
be witnessed before any distinct heart is evolved.

814. The formation of the Heart takes place in the substance of
the Vascular layer ; by a dilatation of the trunk, into which the blood-
vessels unite. At first it appears as a mere excavation, surrounded
by cells ; but its walls gradually acquire firmness and consistency,
and are endowed with a contractile power that enables them to exe-
cute regular pulsations. In this early condition, the heart is known
as the punctum saliens {d, Fig. 132). The first appearance of the
heart in the Chick is at about the 27th hour; the time of its forma-
tion in Mammalia has not been distinctly ascertained.

815. Concurrently with the formation of the Vascular system, the
production of the permanent Digestive cavity commences. This
originates in the separation of a small portion of the yelk-bag, lying
immediately beneath the embryo, from the general cavity, in the fol-
lowing manner. — At about the 25th hour of incubation, in the Fowl's
egg, the parts of the germinal membrane which lie beyond the extre-
mities, and which spread out from the sides of the embryo, are doubled
in, so as to make a depression upon the yelk ; and their folded edges
gradually approach one another under the abdominal surface of the
embryo, so as at last to meet and enclose a cavity, which is at first
simple in its form, but which is subsequently rendered more complex
by the prolongation and involution of its walls in various parts, so as
to form the stomach and intestinal tube (Figs. 133, 134, 135). This
digestive cavity communicates for some time with the yelk-bag (from
which it has been thus pinched off, as it were), by a wide opening,
that is left by the imperfect meeting of the folds of the germinal
membrane that constitute its walls. In the Mammalia, this orifice is
gradually narrowed, and is at last completely closed ; and the yelk-
bag, thus separated, is afterwards thrown off. It may be detected,
however, upon the umbilical cord, up to a late period of pregnancy,
and is known as the Umbilical vesicle. In Birds, and other oviparous

462

FORMATION OF DIGESTIVE CAVITY AND AMNION.

animals, the whole of the yelk-bag is ultimately drawn into the abdo-
men of the embryo ; the former gradually shrinking, as its contents
are exhausted ; and the latter enlarging, so as to receive it as a little
pouch or appendage. In Fishes, the hatching of the egg very com-
monly takes place before the process has been completed ; so that
the little Fish swims about with the yelk-bag hanging from its body.
816. Whilst these processes are going on in the Vascular and Mu-
cous layers of the Germinal membrane, a remarkable change is taking
place in that portion of the Serous lamina, which surrounds the Area
pellucida. This rises up on either side in-^two folds (Fig. 133) ; and

Fig. 133.

Fig. 134.

Diagram of ovum at later stage ; the digestive
cavity beginning to be separated from the yelk-
sac, and the amnion beginning to be formed:— a,
chorion; b, yelk-sac ; c, embryo; d and e, folds
of the serous layer rising up to form the Amnion.

The Amnion in process of formation, by the
arching over of the serous lamina :— a, the cho-
rion; &, the yelk-bag, surrounded by serous and
vascular laminaj; c, the embryo; d, e, and/, ex-
ternal and internal folds of the serous layer, form-
ing the amnion ; g, incipient allantois.

these gradually approach one another, at last meeting in the space be-
tween the general envelop and the embryo, so as to form an addi-
tional investment to the latter. As each fold contains two layers of
membrane, a double envelop is thus formed ; of which the outer layer
(Fig. 134, d, e, and Fig. 135, A), afterwards adheres to the inner sur-
face of the chorion, — the original yelk-bag, or Zona pellucida, being
now lost sight of; whilst the inner one (Fig. 134,y*,y*, and Fig. 135,
jT), remains as a distinct sac, to which the name of Amnion is given.
This takes place during the third day in the Chick ; but the period at
which it occurs in the Human Ovum has not yet been clearly ascer-
tained.

817. The embryo, like the adult, has need of Respiration ; in or-
der that the carbonic acid set free in the Nutritive operations may
be removed from its fluids. In Fishes, the surrounding water acts
with sufficient powder upon the vessels of the yolk-bag, to produce the
required aeration, up to the time when the gills of the young animal
are ready to come into play. But in the higher oviparous animals,
whose development proceeds further before they leave the egg, a
more special provision is made for the purpose. A bag, termed the
allantois, sprouts (as it were) from the lower end of the intestine (Fig.

RESPIRATION OF EMBRYO ;—ALLANTOIS.

463

Fig. 135

134,^); and gradually enlarges, passing round the embryo (Fig
135, g), so as in Birds almost com-
pletely to enclose it, intervening be-
tween the germinal membrane and
the shell, and receiving the direct
influence of the air that penetrates
the latter. It is thus the temporary
lung of the air-breathing oviparous
animal ; and it serves for the aera-
tion of its fluids, up to the time
when it quits the egg. In the Ovum
of the Mammal, the chief office of
the Allantois is to convey the ves-
sels of the Embryo to the Chorion ;
and its extent bears a pretty close
correspondence with the extent of
surface, through which the Chorion
comes into vascular connection with

the Decidua, — this extent varying

Diagram representing a Human Ovura in
second month : — a, 1, smooth portion of cho-
rion; a, 2, villous portion of chorion; k, k,
elongated villi, beginning to collect into Pla-
centa; 6, yolk-sac or umbilical vesicle; c, em-
bryo ; /, amnion (inner layer); §■, allantois;
/i, outer layer of amnion, coalescing with
chorion.

considerably in the different orders
of Mammalia. Thus in the Car-
nivora, whose placenta extends like a band around the whole ovum,
the allantois also lines the whole inner surface of the chorion, except
where the umbilical vesicle comes into contact with it. On the other
hand, in Man and the Quadrumana, whose placenta is restricted to
one spot, the allantois is small, and conveys the foetal vessels to one
portion only of the Chorion. When these vessels have reached the
Chorion, they ramify in its substance, and send filaments into its
villi ; and in proportion as these villi form that connection with the
uterine structure which has been already described (§ 811), do the
vessels increase in size. They then pass directly from the fcetus to
the chorion ; and the allantois, being no longer of any use, shrivels
up like the Yelk-bag, and remains as a minute vesicle, only to be
detected by careful examination. The lower part of it, however,
pinched off (as it w^ere) from the rest, remains as the Urinary blad-
der; and the Urachus or suspensory ligament of the latter represents
the duct, by which the Allantois was originally connected with the
abdominal cavity.

818. The connection which is thus formed between the Vascular
system of the fcetus and that of the parent, is the only one that exists
in the lower Mammalia ; which are thus properly designated as '* non-
placental." Each villus of the Chorion contains a capillary loop ; this
is enclosed in a layer of cells; and this again in a lamina of base-
ment-membrane ; — the whole forming the fcetal tuft. This comes
into contact with the cellular decidua, which lies upon the basement-
membrane covering the vascular layer of the decidua. Now the
Placenta is composed of these very elements, arranged in a more
complex manner. It is formed by an extension of the vascular tufts

464

STRUCTURE OF THE PLACENTA.

of the chorion at certain parts ; and a corresponding adaptation, on
the part of the Uterine structure, to afford to these an increased
supply of nutritious fluid. These specially prolonged portions are
scattered, in the Ruminants and some other Mammalia, over the
whole surface of the Chorion, forming what are termed the Cotyle-
dons; but in the higher orders, and in Man, they are concentrated
in one spot, forming the Placenta. In some of the lower tribes, the
maternal and foetal portions of the placenta may be very easily sepa-
rated ; the former consisting of the thickened decidua ; and the latter
being composed of the prolonged and ramifying vascular tufts of the
Chorion, which dip down into it. But in the Human placenta, the
two elements are mingled together through its whole substance.

819. The Foetal portion of the placenta consists of the branches of
the umbilical vessels; which subdivide at the point at which they
enter the mass, and form, by their minute ramifications, a large part
of its substance. Each villus contains a capillary vessel, which
forms a series of loops, communicating with an artery on the one
side, and with a vein on the other; but the same capillary may enter
several villi, before re-entering a larger vessel. The vessels of the
villi (Fig. 136, g) are covered, as in the chorion, by a layer of cells,
(y*,) enclosed in basement-membrane (e) ; but the foetal tuft thus

Fig. 136.

Fig. 137.

Extremity of a placental villus:— a, external Portion of the external membrane, with the

membrane of the villus, continuous witii the external cells, of a placental villus: — a, cells

lining membrane of the vascular system of the seen through the membrane ; 6, cells seen from

mother; b, external cells of the villus, belonging v^^ithin the villus; e, cells seen in profile along

to the placental decidua; c, c, germinal centres the edge of the villus,

of the external cells; d. the space between the
maternal and foetal portions of the villus; e, the
internal membrane of the villus, continuous with
the external membrane of the chorion;/, the in-
ternal cells of the villus, belonging to the cho-
rion; g, the loop of umbilical vessels.

formed is enclosed in a second series of envelops (a, 6, c), derived
from the maternal portion of the placenta, — a space (d) being left
between the two, however, at the extremity of the tuft. The vas-
cular tufts not unfrequently extend beyond the uterine surface of the
placenta, and dip down into the uterine sinuses, where they are
bathed in the maternal blood. The Maternal portion of the Placenta
may be regarded as a large sac, formed by a prolongation of the
internal coat of the great Uterine vessels. Against the foetal surface
of this sac, the tufts just described may be said to push themselves,

STRUCTURE OF THE PLACENTA.

465

Fig. 138.

Diagram ilJustrating the arrangement of the pla-
cental decidua: — a, decidua in contact with the
interior of the uterus; 6, venous sinus passing ob-
liquely through it by a valvular opening; c, a curling
artery passing in the same direction; rf, the lining
membrane of the maternal vascular system, passing
in from the artery and vein lining the bag of the pla-
centa, and covering e, e, the foetal tufts, passing on to
them from their stems from the foetal side of the
cavity, also by the terminal decidual bars/,/, from
the uterine side, and from one tuft to the other by the
lateral bar, g; h,h, separated foBtal tufts, showing the
internal membrane and cells, which, with the loops-
of umbilical vessels, constitute the true foelal portion
of the tufts.

SO as to dip down into it, carrying before them a portion of its thin
wall, which constitutes a sheath to each tuft. In this manner, the
whole interior of the placental
cavity is intersected by nume-
rous tufts of foetal vessels, dis-
posed in fringes, and bound
down by the membrane that
forms its proper wall, — ^just as
the intestines are covered and
held in their places by the
peritoneum. Now as this di-
latation of the uterine blood-
vessels carries the decidua
before it, every one of the
vascular tufts that dips down
into it will be covered with a
layer of the cellular structure
of the latter (Fig. 137, and
Fig. 138, e) ; and this will also
form a part of all the bands
that connect and tie down the
tufts (Fig. 138,^). The blood
is conveyed into the cavity of
the placenta by the '^ curling
arteries," so named from their

peculiar course (Fig. 138, c), which proceed from the arteries of the
uterus ; and it is returned by large short straight trunks, which pass
obliquely through the decidua (Fig. 138, 6), and discharge their con-
tents into the great uterine sinuses.

820. There is no more direct communication between the Mother
and Foetus than this ; all the observations, which have been supposed
to prove a direct vascular continuity, being certainly fallacious. The
function of the Placenta is manifestly double. The foetal tufts draw,
from the maternal blood, the materials w^hich are required for the
nutrition of the embryo, — these materials having been first selected
and partially elaborated by the two sets of intervening cells : and in
this character, the foetal tufts resemble the villi of the intestinal sur-
face, which dip down into the fluids of the alimentary canal, and
absorb the nutritive material which they furnish. But the Placenta
also serves as a respiratory organ ; aerating the blood of the foetus,
by exposing it to the influence of the oxygenated blood of the Mother :
and in this respect the foetal tufts bear a close correspondence with
the gills of aquatic animals, bringing the blood into relation with a
surrounding fluid medium containing oxygen, which is imbibed by
the blood in exchange for the carbonic acid given ofl".

821. The formation of the Human Placenta commences in the latter
part of the second month of utero-gestation ; during the third, it ac-
quires its proper character; and it subsequently goes on increasing, in

30 : "! vii..

466

CIRCULATION IN FCETUS.

Fig. 139.

o o

K) V

The fcEtal circulation 1. The umbilical cord,
consisting of ihe umbilical vein and two umbilical
arteries : proceeding from the placenta (2). 3. The
umbilical vein dividing into three branches; two
(4. 4) to be distributed to the liver; and one (5), the
ductus venosus, vv^hich enters the inferior vena
cava (6). 7 The portal vein, returning the blood
from the intestines, and uniting with the right
hepatic branch. 8. The right auricle ; the course
of the blood is denoted by the arrow, proceeding
from 8 to 9, the left auricle. 10. The left ventricle ;
the blood following the arrow to the arch of the
aorta (11). to be distributed through the branches
given off by the arch to the head and upper ex-
tremities. The arrows 12 and 13. represent the
return of the blood from the head and upper extre-
mities through the jugular and subclavian veins,
to the superior vena cava (14), to the right auricle
(8). and in the course of the arrow through the
right ventricle (15), to the pulmonary artery (16).
17. The ductus arteriosus, which appears lo be a
proper continuation of the pulmonary artery ; the
offsets at each side are the right and left pulmo-
nary artery cut off; these are of extremely small
size as compared with the ductus arteriosus. The
ductus arteriosus joins the descending aorta (18,
18). which divides into the common iliacs, and
these into the internal iliacs, which become the
hypogastric arteries (19), and return the blood
along the umbilical cord to the placenta; while
the other divisions, the external iliacs (20), are
continued into the lower extremities. The arrows
at the terminations of these vessels mark the re-
turn of the venous blood by the veins to the inferior
cava.

accordance with the growth of the
ovum. The vessels of the Ute-
rus undergo great enlargement
throughout; but especially at the
part to which the Placenta is at-
tached ; and the blood, in moving
through them, produces a peculiar
murmur, which is usually audible
with distinctness at an early period
of pregnancy, and which may be
regarded (when due care is taken
to avoid sources of fallacy) as one
of its most unequivocal physical
signs. The sound is most com-
monly heard near the situation of
the Fallopian tube of the right
side ; and it corresponds with the
pulse of the mother.

822. It would be inconsistent
with the character and objects of
this Treatise, to follow, in any
detail, the history of the develop-
ment of the Foetus, during its
intra-uterine life ; and a general
account of the evolution of most
of the chief organs, is given in
connection with that of their struc-
ture. The condition of the Cir-
culating apparatus, however, at
the period of birth, deserves espe-
cial notice. A general account of
the development of the simple
pulsating trunk, which constitutes
its first form, into the four-cavitied
heart of the higher Vertebrata, —
and of the conversion of the single
trunk proceeding from it, with its
four pairs of branchial arches,
into the aorta and pulmonary arte-
ries, with their chief subdivisions,
has been already given (§ ^^6).
Up to the time of birth, however,
the partition between the Auricles
is incomplete ; a large aperture,
the foramen ovale^ existing in it.
There is also a direct communi-
cation between the pulmonary
artery and the aorta, by the ductus
arteriosus; and another direct

F(ETAL CIRCULATION. 467

channel between the umbilical vein and the vena cava, by the ductus
venosus.

823. The following is the course of the Circulation of the Blood in
the Foetus. The fluid brought from the placenta by the umbilical
vein (Fig. 139, 3), is partly conveyed at once to the vena cava as-
cendens, by means of the ductus venosus (5), and partly flows through
two trunks (4, 4), that unite with the portal vein (7), returning the
blood from the intestines, into the substance of the liver, thence to be
returned to the vena cava by the hepatic vein. Having thus been
ti*ansmitted through the two great depurating organs, the placenta and
the liver, the blood that enters the vena cava is purely arterial in its
character ; but being mixed in the vessels with the venous blood that
is returned from the trunk and lower extremities, it loses this character
in some degree, by the time that it reaches the heart. In the right
auricle, which it then enters, it would also be mixed with the venous
blood which is brought down from the head and upper extremities by
the descending cava ; were it not that a very curious provision exists^
to impede (if it does not entirely prevent) any further admixture.
This consists in the arrangement of the Eustachian valve; which
directs the arterial current (that flows upwards through the ascending
cava) into the left side of the heart, through the foramen ovale :
whilst it directs the venous current (that is being returned by the
descending cava) into the right ventricle. When the ventricles con-
tract, the arterial blood contained in the left is propelled into the
ascending Aorta, and supplies the branches that proceed to the head
and upper extremities, before it undergoes any further admixture :
whilst the venous blood contained in the right ventricle, is forced
into the Pulmonary artery, and thence through the ductus arteriosus
(17) which is like a continuation of its trunk, into the descending
aorta, mingling with the arterial current which that vessel previously
conveyed, and thus supplying the trunk and lower extremities with a
mixed fluid. A portion of this is conveyed, by the umbilical arteries,
to the Placenta; in which it undergoes the renovating influence of
the maternal blood ; and from which it is returned in a state of purity.

824. Hence the head and superior extremities, whose development
is required to be in advance of that of the lower, are supplied with
blood nearly as pure as that which returns from the placenta ; whilst
the rest of the body receives a mixture of this, with what has pre-
viously circulated through the system. The Pulmonary arteries con«
vey little or no blood through the lungs ; the current of blood, pro-
per H from the right ventricle, passes directly onwards through the
ductus arteriosus, into the aorta. — At birth, however, the course of
the circulation undergoes great changes, that it may be adapted to
the new mode, in which the infant is henceforth to obtain its nutrition
and to carry on its respiration. As soon as the lungs are distended
by the first inspiration, a portion of the blood of the pulmonary artery
is diverted into them, and there undergoes aeration ; and, as this pro-
portion increases, with the full actiyity of the lungs, the ductus arte-

468 LENGTH OF GESTATION.

riosus gradually shrinks, and its cavity finally becomes obliterated.
At the same time, the foramen ovale is closed by a valvular fold ; and
thus the direct communication between the two auricles is cut off.
When these changes have been accomplished, the circulation which
was before carried on upon the plan of that of the higher Reptiles
(§ 563) becomes that of the complete warm-blooded animal ; all the
blood which has been returned in a venous state to the right side of
the heart, being transmitted through the lungs, before it can reach
the left side, or be propelled from its arterial trunks. — It is by no
means unfrequent, however, for some arrest of development to pre-
vent the completion of these changes ; and various malformations,
involving an imperfect discharge of the circulating and respiratory
functions, may hence result.

825. The average length of time, which elapses between Concep-
tion and Parturition, in the Human female, appears to be 280 days,
or 40 weeks. There can be little doubt, however, that Gestation
may be occasionally prolonged for one, two, or even three weeks,
beyond that period ; such prolongation not being at all unfrequent
amongst the lower animals ; and numerous well-authenticated in-
stances of it, in the Human female, being upon record. Upon what
circumstances this departure from the usual rule is dependent, has
not yet been ascertained ; but it is a remarkable circumstance, ascer-
tained by the observations of cattle-breeders, that the male has an
influence upon the length of gestation, — a large proportion of cows
in calf by certain bulls exceeding the usual period, and a small pro-
portion falling short of it. Hence we must attribute the prolongation
of the period to some peculiarity in the embryo, derived from its male
parent.

826. The shortest period at which Gestation may terminate, con-
sistently with the life of the child, has not been precisely ascertained ;
the difficulty of determining the precise date of conception being
•usually such, in this case as in the preceding, as to prevent the exact
length of the Gestation from being known. Thus, the commence-
ment of pregnancy being fixed by the time of the cessation of the
Catamenia, when there is no more definite guide, it is obvious that
the act of Conception may have taken place during any part of the
interval that has elapsed since the last monthly period ; and thus a
doubt may exist as to the length of the Gestation, to the extent of
from one to three weeks. There are very satisfactory cases on record,
in which, from the degree of development of the infant at birth, as
well as from other circumstances, it might be certainly known not
to have attained 26 or 27 weeks, or little more than six months ;
and in which, by careful treatment, the infant was reared in a con-
dition of health and vigour. And there is reason to believe, that
infants have lived for some time, and might probably have been
reared under better management, that were born as early as the 24th
or 25th week.

827. The act of Parturition, by which the foetus is expelled from

I

ACT OF PARTURITION. 469

the Uterus, is accomplished in part by the contractile power of the
Uterus itself; and in part by the combined operation of the various
muscles, which press upon the abdominal cavity, and which effect
the expulsion of the feces and urine. No account can be given of
the reasons, why this change should take place at the period, which
has been mentioned as its usual date ; but we are as much in the
dark in regard to other periodic phenomena of Animal life. For
some days previously to the commencement of labour, there is usually
a slow contraction of the fibres of the fundus and body of the uterus ;
and a yielding of those of the cervix ; so that the child lies lower,
and the size of the abdomen diminishes. This slow contraction is
probably not dependent upon any act of the nervous system ; but
upon the direct excitement of the contractility of the muscular sub-
stance of the uterus. When labour properly commences, however,
the Spinal system of nerves comes into play, and the uterine contrac-
tions are of a reflex nature. As before, however, the act of contrac-
tion is confined to the fundus and body of the uterus ; the fibres of the
cervix uteri, and of the vagina, being in a state of relaxation, which
allows them to yield to the pressure of the child's head. In the first
stage of labour, the Uterine contractions appear to be alone concerned ;
and it is not until the head of the child is passing through the os uteri,
and is entering the vagina, that the assistance of the abdominal mus-
cles is called in. These act, in the first instance, as in ordinary
expiration ; but their power is much increased by the voluntary reten-
tion of the breath, so that the whole of their contractile force may be
applied to the expulsion of the foetus. In a latter stage of labour, this
retention of the breath becomes involuntary, during the accession of
the " pains ;" and the expulsion of the foetus is commonly effected
with considerable force, especially if the previous resistance has been
considerable.

828. The same action which expels the foetus, usually detaches the
placenta; and if the uterus contract with suflScient force, after this has
been thrown off, the orifices of the vessels which communicated with
it are so effectually closed, that little or no hemorrhage from that
source takes place. When efficient contractions do not occur, they
may frequently be excited by pressure upon the uterus itself; by the
application of cold to the abdominal surface, to the extremities, and
(in severe hemorrhage) to the entire body: or by the application of the
child to the nipple, which will frequently at once succeed in producing
the desired effect. The efficacy of these means, — the latter in parti-
cular,— obviously depends upon the influence of the spinal system of
nerves upon the muscular fibres of the uterus ; the application of cold
to the surface, or the irritation of the nipple, occasioning a reflex
action in the uterus. But it is probable that this organ has also con-
siderable power of contracting, independently of the nervous system;
thus there are w^ell-authenticated cases on record, in which the foetus
has been expelled after the somatic death (§ 65) of the parent; which
must have been in consequence of the persistence of the independent

470 MAMMARY GLANDS.

contractility of the Uterus, and the relaxed state of all the parts
through which the child had to make its exit.

829. The cause of the occasional occurrence of the parturient efforts
at an unusually early period, is as little understood as that of their
ordinary action. There are some individuals, in whom this regularly
happens at a certain month ; so that it seems to be an action natural
to them. In many cases, however, it may be traced to some undue
exertion of body, or mental excitement; and not unfrequently to a
general constitutional irritability, which renders the system liable to
be deranged by very trifling causes. Premature labour is almost always
to be prevented, if possible; being injurious alike to both mother and
child ; and for this prevention we have chiefly to rely upon rest and
tranquillity of mind and body, and upon the careful avoidance of all
those exciting causes, which are liable to produce uterine contractions
by their operation upon the nervous system ; whilst, at the same time,
any measures which will invigorate the body, without stimulating it,
should not be overlooked.

830. A peculiar preparation is made, in the females of the class
Mammalia, for the sustenance of the infant, for a long period after
birth. This consists in the secretion of a fluid, from the glands, termed
Mammary^ which contains all the elements that are required for the
development of the body of the infant, during the first year. These
glands present themselves in an almost rudimentary state, in some of
the non-placental animals of the class ; consisting only of a few large
follicles, which open separately upon the surface (Fig. 106). In the
higher Mammalia, however, we find it composed of vast numbers of
minute follicles, clustered together upon excretory ducts. The general
arrangement of these, in the human subject, is seen in Fig. 140; and

in Fig. 11 1, the character of the follicles them-
F'"!"^^- selves, and of the secreting epithelial cells they

contain, as seen under a much higher magni-
fying power, has been already shown. Each
Mammary gland consists of a number of glan-
dulae, which are held together by areolar and
fibrous tissue ; this arrangement may probably
have reference to the mobility, which it is re-
miikXcMn^foUicirsffmrn^a quisitc that the different parts of the mass should
"S^^l^^^l^^s!" possess, one upon the other, in consequence of
its situation upon the pectoralis muscle. The
ducts converge and unite together; so as at last to form ten or twelve
principal trunks, which terminate in the nipple. At the base of the
nipple, these tubes dilate into reservoirs, which extend beneath the
areola, and to some distance into the gland, when the breast is in a
state of lactation. These, which are much larger in many of the
lower Mammalia than they are in the Human female, seem to have
for their office to contain a store of milk, sufl^cient to supply the imme-
diate wants of the child when it is first applied to the breast; so that

COMPOSITION OF MILK. 471

it shall not be disappointed, but shall be induced to proceed with
sucking, until the draught be occasioned (§ 836).

831. The Mammary gland may be detected at an early period of
foetal existence, and it then presents no difference in the male and
female ; and it continues to grow, in each sex, in proportion to the
body at large, up to the period of puberty. At that epoch, however,
the gland begins to undergo a great enlargement in the female ; and by
the age of twenty, it attains its full size previous to lactation. Even
then, however, the milk-follicles cannot be injected from the tubes.
During pregnancy, the mammary glands receive a greatly-increased
quantity of blood. This determination often commences very early ;
and produces a feeling of tenderness and distension, which is a valuable
sign (where it occurs in conjunction with others) of conception having
taken place. The vascularity of the gland continues to increase during
pregnancy; and, at the time of parturition, its lobulated character can
be distinctly felt. The follicles cannot be readily injected, however,
until the gland is in a state of complete functional activity ; i. e., during
lactation. — The Mammary gland of the Male does not undergo this
increase of development, except under certain peculiar circumstances
to be presently noticed (§ 836); and it remains a sort of miniature
picture of that of the female, varying in diameter from that of a large
pea to an inch or even two inches.

832. The Milk, secreted by the Mammary glands, consists of
Water, holding in solution the peculiar albuminous substance termed
Casein (§ 176), and various Saline ingredients, together with (in
most cases) a certain form of Sugar; and having Oleaginous globules
suspended in it. These globules appear to be surrounded by a thin
pellicle, which keeps them asunder, so long as the milk remains at
rest. — The existence of these elements in ordinary Milk, as that of the
Cow, is made apparent by the processes to which it is subjected in
domestic economy. If it be allowed to stand for some time, exposed
to the air, a large part of the oleaginous globules come to the surface,
in consequence of their inferior specific gravity ; and thus is formed
the creamy which includes also a considerable amount of casein, with
the sugar and salts of the milk. These may be partly separated by
the continued agitation of the cream, as in the process of churning;
this, by rupturing the envelops of the oil-globules, separates it into
butter, formed by their aggregation, and buttermilk, containing the
casein, sugar, &c. A considerable quantity of casein, however, is
still entangled with the oleaginous matter ; and this has a tendency
to decompose, so as to render the butter rancid. It maybe separated
by keeping the butter melted at a temperature of 180° ; when the
casein will fall to the bottom, leaving the butter pure and much less
liable to change, — an operation which is commonly known as the
clarifying of butter. The Milk, after the cream has been removed,
still contains the greater part of its casein and sugar. If it be kept
long enough, a spontaneous change takes place in its composition ; an
incipient change in the casein being the cause of the conversion of

472 COMPOSITION OF MILK.

the sugar into lactic acid ; and this coagulating the casein, by pre-
cipitating it in small flakes. The same precipitation may be accom-
plished at any time by the agency of various acids, especially the
acetic, which does not act upon Albumen ; but Casein cannot be
coagulated like albumen, by the influence of heat alone. The most
complete coagulation of Casein is effected by the agency of the dried
stomach of the calf, known as rennet; which exerts so powerful an
influence, as to coagulate the casein of 1,800 times its weight of
milk. It is thus that, as in the making of cheese, the curd is sepa-
rated from the whey; the former consisting chiefly of the casein;
whilst the latter contains a large proportion of the saline and saccha-
rine matter, which entered into the original composition of the milk.
These may be readily separated by evaporation.

833. The chief characters of Casein have been already stated
(§ 176). — Its Oleaginous matter consists, like the fats in general, of
the two substances, elaine and stearine ; but it also contains another
substance peculiar to it, which is termed hutyrine. This last (to
which the characteristic smell and taste of butter are due) is converted
by saponification into three volatile acids, of strong animal odour, to
which the names of butyric, capric, and caproic acids have been given.
This change may be effected, at any period, by treating the butyrine
with alkalies ; but it may also take place by spontaneous decompo-
sition, which is favoured by time and moderate warmth. — The Sugar
of Milk is peculiar as containing nearly 12 per cent, of water; so that
it may be considered as really a hydrate of sugar. It is nearly iden-
tical in its composition with starch ; and may, like it, be converted
into true sugar by the agency of sulphuric acid. But it is chiefly re-
markable for its proneness to conversion into lactic acid, under the
influence of a ferment or decomposing azotized substance. — The Sa-
line matter contained in Milk appears to be nearly identical with that
of the blood ; with a larger proportion, however, of the phosphates of
lime and magnesia, which amount to 2 or 2\ parts in 1000. These
are held in solution chiefly by the Casein, which has a remarkable
power of combining with them.

834. Thus ordinary Milk contains the three classes of organic
principles, which form the chief part of the food of animals, — namely,
the albuminous, the saccharine, and the oleaginous; together with the
mineral elements, which are required for the development and consoli-
dation of the fabric of the infant. It would appear, however, that
the combination of all these is not necessary; but rather has reference
to the composition of the food, on which the animal is destined to be
afterwards supported. Thus it has been lately shown that, in the
Carnivora, the milk contains no sugar ; which principle is altogether
wanting in the food of the adult. Amongst the different species of
Herbivorous animals, the proportion of the several ingredients varies
considerably ; and it is also liable to considerable variation in accord-
ance with the nature of the food, the amount of exercise taken by the
animal that affords it, and other circumstances. Thus in the milk of

COMPOSITION AND PRODUCTION OF MILK. 473

the Cow, Goat, and Sheep, the average proportions of Casein, Butter,
and Sugar are nearly the same one with another, each amounting to
from 3 to 5 per cent. In the milk of the Ass and Mare, on the
other hand, the proportion of Casein is under 2 per cent., the oleagi-
nous constituents are scarcely traceable, whilst the sugar and allied
substances rise to nearly 9 percent. In the Human female, the sac-
charine and oleaginous elements are both present in large amount;
whilst the Casein forms a moderate proportion. — The proportion of
the saccharine and oleaginous elements appears to be considerably
affected by the amount in which these are present in the food ; and
by the degree in which the quantity ingested is consumed by the
respiratory process. Thus, a low external temperature, and out-door
exercise, by increasing the production of carbonic acid from the lungs,
occasion the consumption of the oleaginous and saccharine matters,
which might otherwise pass into the milk, and thus diminish the
amount of cream. On the other hand, exercise favours the secretion
of casein ; which would seem to show, that this ingredient is derived
from the disintegration of the azotized tissues. Thus in Switzerland,
the cattle which pasture in exposed situations, and which are obliged
to use a great deal of muscular exertion, yield a very small quantity
of butter, but an unusually large proportion of Cheese ; yet the same
cattle, when stall-fed, give a large quantity of butter, and very little
cheese.

835. The Milk first secreted after parturition, known as the Colos-
trum^ is very different from ordinary milk ; and possesses a strongly
purgative action, which is useful in clearing the bowels of the infant
from the various secretions which have accumulated in them at birth^
constituting the meconium. The Colostrum, when examined with the
Microscope, is found to contain a multitude of large yellow granulated
corpuscles ; each of which seems composed of a number of small grains
aggregated together. The colostric character is sometimes retained for
some time after birth, and severely affects the health of the infant.
This may happen without any peculiarity in the ordinary characters
of the secretion, which has all the appearance of healthy milk ; but
the Microscope at once detects the difference, by the presence of the
colostric corpuscles.

836. The formation of this Secretion is influenced by the Nervous
system, to a greater degree, perhaps, than that of any other. The
process may go on continuously, to a slight degree, during the whole
period of lactation ; but it is only in animals that have special reser-
voirs for the purpose, that any accumulation of the fluid can take
place. In the Human female, as we have seen, these are so minute
as to hold but a trifling quantity of milk ; and the greater part of the
secretion is actually formed, whilst the child is at the breast. The
irritation of the nipple produced by the act of suction, and the mental
emotion connected with it, concur to produce an increased flow of
blood into the gland, which is known to Nurses as the draught ; and
thus the secretion is for the time greatly augmented. The draught

474 INFLUENCE OF FEELINGS ON MAMMARY SECRETION.

may be produced simply by the emotional state of mind, as by the
thought of the child when absent ; and the irritation of the nipple
may alone occasion it ; but the two influences usually act simulta-
neously. The most remarkable examples of the influence of such
stimuli on the Mammary secretion, are those in which milk has been
produced by girls and old women, and even by men, in quantity suffi-
cient for the support of an infant. The application of the child to the
nipple in order to tranquilize it, the irritation produced by its efforts
at suction, and the strong desire to furnish milk, seem in the first
instance to occasion an augmented nutrition of the gland, so that it
becomes fit for the performance of its function ; and then to produce
in it that state of functional activity, the result of which is the pro-
duction of Milk.

837. It is not only in this way, that the Mammary secretion is in-
fluenced by the condition of the mind ; for it is peculiarly liable to be
aflfected as to quality, by the habitual state of the feelings, or even by
their temporary excitement. Thus a fretful temper not only lessens
the quantity of milk, but makes it thin and serous, and gives it an
irritating quality ; and the same effect will be produced for a time by
a fit of anger. Under the influence of grief or anxiety, the secretion
is either checked altogether, or it is diminished in amount, and dete-
riorated in quality. The secretion is usually checked altogether by
terror ; and under the influence of violent passion, it may be so changed
in its characters, as to produce the most injurious and even fatal con-
sequences to the infant. So many instances are now on record, in
which children, that have been suckled within a few minutes after the
mothers have been in a state of violent rage or terror, have died sud-
denly in convulsive attacks, that the occurrence can scarcely be set
down as a mere coincidence ; and certain as we are of the deleterious
effects of less severe emotions upon the properties of the milk, it does
not seem unlikely that, in these cases, the bland nutritious fluid should
be converted into a poison of rapid and deadly operation.

838. Of the quantity of Milk ordinarily secreted by a good Nurse,
it is impossible to form any definite idea ; as the amount which can
be artificially drawn, affords no criterion of that which is ordinarily
secreted at the time of the draught. The quantity which can be
squeezed from either breast at any one time, and which, therefore,
must have been contained in its tubes and reservoirs, is about two
ounces. The amount secreted will depend upon several circum-
stances ; such as the nature and amount of the ingesta ; the state of
bodily health ; and the condition of the mind. An adequate but not
excessive amount of nutritious food, in which the farinaceous, olea-
ginous, and albuminous principles are duly blended ; a vigorous but
not plethoric constitution, regular habits, and moderate exercise ;
together with a cheerful and tranquil temper ; altogether produce the
most beneficial influence upon the secretion. It is seldom that stimu-
lating liquors, which are so commonly indulged in, are anything but
prejudicial ; but the unmeasured condemnation of them, in which

ELEMENTS OF MILK PRE-EXISTENT IN BLOOD. 475

some writers have indulged, is certainly injudicious ; as experience
amply demonstrates the improvement in the condition both of mother
and infant, which occasionally results from the moderate employment
of them. — In the administration of medicines to the mother, it is
very desirable that the tendency of soluble saline substances to pass
into the milk, and thus to affect the child, should be borne in mind.
The vegetable substances used in medicine seem to have much less
disposition to pass off by this secretion ; and they are consequently
to be preferred during lactation.

839. From the close correspondence which exists between the ele-
ments of the Milk and those of the Blood, it is evident that we cannot
expect to trace the existence of the former, as such, in the circulating
current. It is interesting, however, to remark, that a preparation ap-
pears to be taking place in the laboratory of the system, for the pro-
duction of this secretion, long before the period of parturition. The
Urine of pregnant women almost invariably contains a peculiar sub-
stance termed kiestine, which is nearly related to casein, and which
disappears from the urine as soon as lactation has fully commenced.
It would seem, therefore, that a compound of this nature is in course
of preparation during pregnancy ; and that it is eliminated by the
kidney until the Mammary Gland is prepared for the active perform
ance of its function. — That the kidney may relieve the system from
the accumulation of other constituents of the mammary secretion, ap-
pears from a case recently put on record ; in which the urine of a par-
turient female, who did not suckle her infant, was found to contain a
considerable quantity of butyric acid, during several days. There
can be no doubt that in ordinary states of the system, this secretion
cannot be required for the depuration of the blood ; since it does not
occur in the male at all, and is present in the female at particular times
only. But these facts afford ground to believe that, when the process
is going on, certain products are generated in the system, which are
not found there at other times. And it is quite certain that the sud-
den checking of the secretion, or the re-absorption of the fluid already
poured out, occasioning an accumulation of these substances in the cir-
culating current, may give rise to very injurious consequences. Some
very curious instances are on record, in which a transference of the
secreting power to some other surface has taken place under such cir-
cumstances ; so as to relieve the system from the accumulation in
question.

476 GENERAL FUNCTIONS OF NERVOUS SYSTEM,

CHAPTER XII.

OF 1"HE NERVOUS SYSTEM.

1, General View of the operations, of which the JVervous System is the

instrument.

840. We have now considered the entire series of those operations,
which niake up the vegetative or organic life of the Animal; including
the functions by which the germ is prepared, by which it is nourished
until it can be left to its own powers, by which its continued deve-
lopment is effected until the fabric characteristic of the adult has been
built up, and by which the normal constitution is maintained through
a lengthened period, — so long as the necessary materials are supplied,
and no check or hindrance is interposed, by external influences, to that
regular sequence of change, on which the continuance of its powers
depends. In this survey it will have been perceived, that the essential
parts of these operations are, in Animals as in Plants, completely
independent of the influence of that, which constitutes the peculiar
endow^ment of Animals; namely, the Nervous System.

a. The Reduction of the food in the Stomach, by the solvent power
of the gastric fluid, is a purely chemical operation, with which the
Nervous System has nothing whatever to do, excepting that it per-
haps accelerates the process, by stimulating the Muscular coat of the
stomach to that peculiar series of contractions, which keeps the con-
tents of the cavity in continual movement, and favours the action of
the solvent upon it.

b. With the process of Absorption, by which the nutritive materials,
with other substances, are introduced into the vessels, the Nervous
System has nothing to do ; this being a purely vegetative operation,
partly dependent upon the simple physical conditions which produce
Endosmose, and partly on a process of cell-growth.

c. The Assimilation of the new material, effected, as we have seen
reason to believe, by another set of independent cells, can receive but
little influence from the Nervous System, and is obviously capable
of taking place without its aid.

d. The Circulation of the Blood, again, though dependent in part
upon the impulsive power of a Muscular organ, the Heart, is not on
that account brought into closer dependence upon the Nervous System;
for we have seen that the contractions of the heart result from its own
inherent powers, so as to continue after it has been completely de-
tached from the body ; and that the capillary power, which is the chief
agent in the movement of the blood in the lower animals, and which
exerts an important subsidiary action in the higher, is the result of

GENERAL FUNCTIONS OF NERVOUS SYSTEM. 477

the exercise of certain affinities, between the blood and the surround-
ing tissues, in which the Nervous System can have no immediate
concern.

e. The act of JVutrition, in which every tissue draws from the cir-
culating blood the materials for its own continued growth and deve-
lopment, and by which it incorporates these with its own substance,
is but a continuance of the same kind of operation, as that which
takes place in the early development of the embryo, long anteriorly to
the first appearance of the nervous system, — namely, a process of cell-
development and metamorphosis, which must be, from its very nature,
independent of Nervous agency.

y. The same may be said of the Secreting operation in general ; for
this essentially consists of the separation of certain products from the
blood, by cells situated upon free surfaces; which thus remove those
products from the interior of the fabric.

g. And the interchange of oxygen and carbonic acid, w^hich takes
place between the atmosphere and the venous blood, when brought
into mutual relation in the lungs, and which is the essential part of the
function of Respiration^ is an operation of a merely physical character,
with which the Nervous system can have no direct concern.

h. Finally, the development of the reproductive germs in the one
sex, and of the ova within which these are to be evolved in the other,
the subsequent fertilization of the latter by the former, and the changes
consequent upon that act, together making up the function of Repro-
duction, may be all regarded as modifications of the ordinary Nutri-
tive processes; and are effected, like these, by the inherent powers
of the parts concerned in them, at the expense of the materials sup-
plied by the blood, without any direct dependence upon the Nervous
system.

841. Still, although the various processes, which make up the essen-
tial part of the nutritive operations, in Animals as in Plants, are no
more dependent on any peculiar influence derived from a Nervous
system, in the former, than they are in the latter, it must be evident,
from the details already given, that there must be in Animals various
accessory changes, which are requisite for the continuance of the
former, and which can only be effected by the peculiar powers with
which Animals are endowed. — Thus, to commence with Digestion ; —
this preliminary process, which the nature of the food of the plant
renders unnecessary {ox its maintenance, can only be accomplished by
the introduction of the food into a cavity or sac, in which it may be
submitted to the action of the solvent fluid. The operation o{ grasp-
ing and swallowing the food, wherever it is performed, is accomplished
through the agency of the Nervous system ; and if it be checked by
the loss of Nervous power, the Digestive process must cease for want
of material. — So, again, although interchange of gaseous ingredients
between the atmosphere and the circulating fluid may take place with
sufficient energy in Plants and the lower Animals, through the mere
exposure of the general surface to the atmosphere, yet w^e find that,

478 SHARE OF NERVOUS SYSTEM IN ORGANIC FUNCTIONS.

in all the higher Animals, certain movements are requisite, for the con-
tinual renewal of the air or water which are in contact with one side
of the respiratory surface, and of the blood which is in relation with
the other : for the direction of which movements, a Nervous system
is requisite. — In the excretory processes, moreover, the removal of the
effete matters from the body can only be accomplished, in the higher
Animals, by certain combined movements; the object of which is to
take up the products that are separated by the action of the proper
secreting cells, and to carry them to the exterior of the body, there
to be set free ; and these combined movements can only be effected
by the agency of the Nervous system. — Lastly, in the act of Repro-
duction, the arrangement of the sexual organs in Animals, requires
that a certain set of movements should be adapted to set free the germ
from the body of the male, and to convey it to the ovule of the fe-
male; and further, that the ovum should be expelled from the body
of the latter, in a state of more or less advanced development. For
these movements a special arrangement is made, in the construction
of the Nervous system, and in the application of its peculiar powers.
842. Thus we see that, although the Organic functions of the Ani-
mal are essentially independent of the Nervous System, this system
affords the conditions which are requisite for their continued main-
tenance ; being the instrument by which the muscles are called into
action for the performance of the various combined actions that con-
stitute the mechanism (so to speak), by which the Vegetative part of
the fabric is combined w^ith the Animal portion of the organism. We
are not to suppose, however, that every movement which takes place
in the Animal body is dependent upon the Nervous System ; for we
have seen that the Muscular tissue may be employed to perform con-
tractions excited by stimuli applied to itself, and that it may thus
execute a set of movements in which the nervous system has no di-
rect participation. And it is desirable that the Student should ob-
serve, that these are, in all instances, those most directly connected
with the Vegetative functions, and, at the same time, those of the
simplest and most straightforward character. — Thus, the peristaltic
movement, by which the alimentary and fecal matters are propelled
along the Intestinal tube, results from the direct excitement of the
contractility of its muscular walls, and is entirely independent of
Nervous agency ; and this movement is accomplished by the succes-
sive contraction of the different fasciculi surrounding the tube, which
take up (as it were) each other's action (§ 352). So, again, the suc-
cessive contractions and dilatations of the cavities of the Heart, which
perform so important a part in the Circulation of the blood, are the
result of the properties inherent in that organ ; the muscular fibres of
which are excited to a peculiar rhythmical and consentaneous con-
traction, by the flow of blood into the cavities when dilating. More-
over, in the Excretory ducts of various glands, we find a Muscular
coat, by which the fluids secreted in the glands, are propelled towards

GENERAL FUNCTIONS OF NERVOUS SYSTEM. 479

their outlet on the exterior of the body, or on one of its free internal
surfaces.

843. In these instances, then, we observe that the simple Contrac-
tility of Muscular structure, excited by direct stimulation, is applied
to effect the movements most closely connected with the Organic
functions. With the processes, therefore, which take place in the
penetralia of the system, the Nervous System has no direct concern.
Its office is to guard the portals for entrance and exit ; and to fill
those chambers, which admit the new materials from the external
world ; or to empty the receptacles, which collect from the interior of
the system the effete matters that are to be cast out from it. And we
find that, for these offices, the Nervous system is employed in its very
simplest mode of operation ; — that which does not involve Sensation,
Intelligence, Will, or even Instinct (in the proper sense of that term),
but which may take place independently of all consciousness, — by the
simple reflexion of an impression, conveyed to a ganglionic centre by
one set of fibres proceeding towards it from the circumference along
another set which passesyrom it to the muscles, and calls them into
operation (§ 394). This reflex function, therefore, is the simplest
application of the Nervous System in the Animal body. We shall
presently see reason to believe, that a very large proportion of the
movements of many of the lower animals are of this reflex character ;
and that they are not necessarily accompanied by sensation, although
this may usually be aroused by the same cause which produces them.
As we rise, however, in the scale of Animal existence, we find the
reflex movements forming a smaller and smaller proportion of the
whole ; until, in Man, they constitute so limited a part of the entire
series of movements of which the Nervous system is the agent, that
their very existence has been overlooked.

844. But the main purpose of the Nervous System is to serve as
the instrument of the Psychical* powers, which are the distinguishing
attribute of the Animal. It has been already pointed out, that the pos-
session of Consciousness (or of the capability of receiving sensations),
and the power of executing Spontaneous Movements (that is, move-
ments which are not immediately dependent upon external stimuli), con-
stitute the essential features in which the Animal differs from the Plant.
All the other differences in structure, that respectively characterize
these two classes of living beings, are subordinate to this one leading
distinction, — the presence of a Nervous system, and of its peculiar
attributes in the one, — and its absence in the other. Now when we
attempt to analyze these peculiar attributes, we may resolve them,
like the properties of the material body, into different groups. We
find that the first excitement of all mental changes, whether these
involve the action of (he Jeelings or of the reason, depends upon sen-
sations ; which are produced by impressions made upon the nerves of

* This term, derived from the Greek ^-w^"* is used to designate the sensorial and
mental endowments of Animals, in the most comprehensive acceptation of those
terms.

480 DEPENDENCE OF MENTAL ACTIONS UPON SENSATION.

certain parts of the body, and are conveyed by these to a particular
ganglionic centre, which is termed the sensorium, — being the part in
which Sensation, or the capability oi feeling external impressions,
especially resides.

845. Now there are numerous actions, especially among the lower
Animals, which seem to be as far removed from the influence of the
Will, and as little directed by Intelligence, as the Reflex movements
themselves ; but which, nevertheless, depend upon sensation for their
excitement. The sensation may immediately direct the movement ;
or it may excite an emotion or desire, which, without any calculation
of consequences, any intentional adaptation of means to ends, any
exertion of the reason, or any employment of a discriminating Will,
may produce an action, or train of actions, as directly and obviously
adapted to the well-being of the individual, as we have seen those of
the reflex character to be. It is impossible to say, in regard to many
of the actions of the lower animals, to what extent they involve feel-
ings or emotions, at all analogous to those which we experience ; and
it would seem better to apply the generic term Consensual to those in
which the Sensation excites the motor action, either immediately, or
through the agency of an indiscriminating Desire excited by the sen-
sation. This class will include all the purely Instinctive actions of
the low^er Animals ; which make up, with the reflex, nearly the whole
of the Animal functions in many tribes ; but which are found to be
gradually brought under subordination to the Intelligence and Will,
as we rise towards Man, in whom those faculties are most strongly
developed, so as to keep the Consensual as well as the Reflex actions
quite in subordination to the more elevated purposes of his existence.

846. There are many sensations, however, which do not thus im-
mediately give rise to muscular movements ; their operation being
rather that of stimulating to action the Intellectual powers. There
can be little doubt that all Mental processes are dependent, in the first
instance, upon Sensations ; which serve to the Mind the same kind of
purpose, that food and air fulfil in the economy of the body. If we
could imagine a being to come into the world with its mental faculties
fully prepared for action, but destitute of any power of receiving sen-
sations, these faculties would never be aroused from the condition in
which they are in profound sleep ; and the being must remain in a
state of complete unconsciousness, because there is nothing of which
it can be made conscious, no kind of idea which can be aroused
within it. But after the mind has once been in active operation, the
destruction of all future power of receiving sensations would not
reduce it again to the inactive condition. For sensations are so stored
up in the mind, by the power of Memory, that they may give rise to
ideas at any future time ; and thus the mind may feed (as it were)
upon the past. Now the ideas which are excited by sensations, and
which are coloured by the state of Feeling which accompanies them,
become the subjects of Reasoning processes more or less complex,
sometimes of the utmost brevity and simplicity, sometimes of the most

I

CLASSIFICATION OF ACTIONS OF NERVOUS SYSTEM. 481

refined and intricate nature. These reasoning processes, when they
result in a determination to execute a particular movement, execute
that movement by an act of Volition ; the peculiar character of which
is, that it is the expression of a definite purpose, of a designed adapta-
tion of means to ends, on the part of the individual performing it ;
instead of being the result of mere blind indiscriminating impulse,
which seems to be the main-spring of the instinctive operations. It
is in Man, that we find the highest development of the reasoning
faculties ; but it is quite absurd to limit them to him, as some have
done ; since no impartial observer can doubt, that many of the lower
animals can execute reasoning processes, as complete in their way as
those of Man, though much more limited in their scope.

847. Thus, then, we have to consider the Nervous system under
three heads ;— first, as the instrument of the Reflex actions ; — second,
as the instrument of the Consensual and Instinctive actions ; — third,
as the instrument of the Intellectual processes, and of Voluntary
movements. Now there is good reason to believe, that to each of
these groups of actions a particular portion of the Nervous Centres,
with its afferent and efferent nerves, may be assigned ; — one ganglion,
or collection of ganglia, being the instrument of the Reflex actions;
another of the Consensual and Instinctive operations ; and a third of
the Intellectual powers, and of the Voluntary movements to w^hich
they give rise. In order that the relations of these subdivisions may
be better understood, it will be desirable to take a brief survey of the
comparative structure of the Nervous system in the principal groups
of Animals; and to inquire what actions may be justly attributed to
its several parts in each instance ; commencing with those in which
the structure is the simplest, and the variety of actions the smallest;
and passing on gradually to those, in which the structure is increased
in complexity by the addition of new and distinct parts, and in which
the actions present a corresponding variety.

2. Comparative Structure and Actions of the Jfervous System.

848. From what has been already said (§ 373-9) of the characters
of the two elementary forms of the Nervous Tissue, it is evident that
no Nervous System can exist, in which both these forms should not
be present. We look, therefore, for ganglia, composed of the vesi-
cular nervous substance, and serving as the centres of nervous
power; and for cords or trunks, composed of the tubular substance,
and serving to communicate between the ganglia and the parts with
which they are to be functionally connected. Now it is quite certain
that, at present, no such Nervous apparatus can be detected in many
of the lowest Animals ; and some Physiologists have had recourse to
the supposition of their possessing a " diffused" nervous system, —
that is, of their possessing nervous particles, in a separate form, in-
corporated as it were with their tissues. But we have seen, that each
tissue possesses its own properties, and can perform its own actions,

31

482 NERVOUS SYSTEM OF LOWEST ANIMALS.

independently of the rest; — that even the contractility of Muscular
fibre is by no means dependent upon the Nervous system, though
usually called into play through its means ; — and that the simplest
office of a Nervous System is to produce a muscular movement in
respondence to a certain impression ; which action requires that it
should have an internuncial or communicating power, only to be ex-
ercised (so far as we at present know) by continuous fibres. The
apparent absence of a Nervous system is doubtless to be attributed,
in many instances, to the general softness of the tissues of the body,
which prevents it from being clearly made out among them. And it
is to be remembered, that, on the principles already stated, we should
expect to find it bearing a much smaller proportion to the entire
structure, in the lowest Animals, whose functions are chiefly Vegeta-
tive,— than in the highest, in which the vegetative functions seem
destined merely for the development of the Nervous and Muscular
systems, and for the sustenance of their powers.

849. Among the Radiated classes, the parts of whose bodies are
arranged in a circular manner around the mouth, and repeat each
other more or less precisely, the Nervous system presents a corre-
sponding form. In the Star-fish, for example, which is one of the
highest of these animals, it forms a ring, which surrounds the mouth ;
this ring consists of nervous cords, which form communications
between the several ganglia, one of which is placed at the base of
each ray. The number of these ganglia corresponds with that of the
rays or arms ; being five in the common Star-fish ; and from nine to
fifteen^ in the species possessing those several numbers of members.
The ganglia appear to be all similar to one another in function, as
they are in the distribution of their branches ; every one of them
sending a large trunk along its own ray, and two small filaments to
the organs in the central disk. The rays being all so similar in
structure, as to be exact repetitions of each other, it would appear
that none of the ganglia can have any controlling power over the
rest. All the rays (in certain species) have at their extremities what
seem to be very imperfect eyes ; and so far as these can aid in direct-
ing the movements of the animal, it is obvious that they will do so
towards all sides alike. Hence there is no one part, which corre-
sponds to the head of higher animals ; and the ganglia of the nervous
system, like the parts they supply, are but repetitions of one another,
and are capable of acting quite independently. Each would perform
its own individual functions if separated from the rest ; but, in the
entire animal, their actions are all connected with others by the circular
cord, which passes from every one of the five ganglia to those on
either side of it. We shall find that, in Articulated and Vertebrated
animals, there is a similar repetition of corresponding ganglia, on the
two sides of the median plane of the body ; and that these are con-
nected by transverse bands, analogous in function to the circular cord
of the Star-fish. Moreover, we shall see a like repetition of ganglia,
almost or precisely similar in function, in passing from one extremity

1

I

NERVOUS SYSTEM OF RADIATA AND MOLLUSCA. 483

of these animals to the other ; and these ganglia are connected by lon-
gitudinal cords, whose function is in like manner commissural. — From
the best judgment we can form of the actions of the Star-fish, by com-
paring them with the corresponding actions of higher animals, we
may fairly regard the greater number of them as simply reflex ; being
performed in direct respondence to external stimuli, the impression
made by which is propagated to one or more of the ganglia, and ex-
cites in them a motor impulse. How far the movements of these
animals are indicative of sensation^ we have not the power of deter-
mining; but it may be safely affirmed, that they afford very little
indication, if any, of the exercise of reasoning faculties, or of volun-
tary power.

850. Perhaps the simplest form of a Nervous system is that pre-
sented by certain of the lower Mollusca ; for here, the body not pos-
sessing any repetition of similar parts, the nervous system is destitute
of that multiplication of ganglia which we see in the Star-fish ; whilst
the limited nature of the animal powers involves a corresponding sim-
plicity in the integral parts of their instrument. The animals, to
which reference is here made, form the class Tunicata; which is inter-
mediate, in many respects, between the ordinary Mollusks and the
Zoophytes. They consist essentially of an external membranous bag
or tunic ; within which is a muscular envelop ; and within this, again,
a respiratory sac, which may be considered as the dilated pharynx of
the animal. At the bottom of this last, is the entrance to the stomach;
which, with the other viscera, lies at the lower end of the muscular
sac. The external envelops have two orifices ; a mouth, to admit
water into the pharyngeal sac ; and an anal orifice, for the expulsion
of the water which has served for respiration, and of that which has
passed through the alimentary canal, together with the fecal matter,
the ova, &c. A current of water is continually being drawn into the
pharyngeal sac, by the action of the cilia that line it; and of this, a
part is driven into the stomach, conveying to it the necessary supply
of aliment in a very finely divided state ; whilst a part is destined
merely for the aeration of the circulating fluid, and is transmitted
more directly to the anal orifice, after having served that purpose.
These animals are for the most part fixed to one spot, during all but
the earliest period of their existence; and they give but little external
manifestation of life, beyond the continual entrance and exit of the
currents already adverted to, which, being eflfected by ciliary action, is
altogether independent of the nervous system (§ 224). When any
substance is drawn in by the current, however, the entrance of which
would be injurious, it excites a general contraction of the mantle or
muscular envelop ; and this causes a jet of water to issue from one or
both orifices, which carries the oflfending body to a distance. And,
in the same manner, if the exterior of the body be touched, the
mantle suddenly and violently contracts, and expels the contents of
the sac.

851. These are the only actions, so far as we know, which the

484 NERVOUS SYSTEM OF MOLLUSCA.

Nervous system of these animals is destined to perform. They do not
exhibit the least trace of eyes, or of other organs of special sense ; and
the only parts that appear peculiarly sensitive, are the small tentacula
or feelers, that guard the oral orifice. Between the two apertures in
the mantle, we find a solitary ganglion, which receives branches from
both orifices, and sends others over the muscular sac. This, so far as
we know at present, constitutes the whole nervous system of the
animal ; and it is fully sufficient to account for the movements which
have been described. For the impression produced by the contact of
any hard substance with the tentacula, or with the general surface of
the mantle, being conveyed by the afferent fibres of this ganglion, will
excite in it a reflex motor impulse ; which, being transmitted to the
muscular fibres of the contractile sac, as well as to those circular bands
that surround the orifices and act as sphincters, will produce the
movements in question.

852. In the Conchifera, or Mollusks inhabiting bivalve shells, there
are invariably two ganglia, having diflferent functions. The larger of
these (Plate II, Fig. 1, c), corresponding to the single ganglion of the
Tunicata, is situated towards the posterior end of the body (that is,
the end most distant from the mouth), in the neighbourhood of the
posterior muscle that draws the valves together; and its branches are
distributed to that muscle, to the mantle, to the gills {d, d)^ and to
the siphons (e, e), by which the water is introduced and carried oflf.
But we find another ganglion, or rather pair of ganglia (a, a), situated
near the front of the body, either upon the oesophagus, or at its sides;
these ganglia are connected with the very sensitive tentacula, which
guard the mouth ; and they may be regarded as presenting the first
approach, both in position and functions, to the brain of higher ani-
mals. In the Oyster, and others of the lower Conchifera, which
have no foot, these are the only principal ganglia ; but in those hav-
ing a foot, — which is a muscular tongue-like organ, — we find an addi-
tional ganglion (6) connected with it. This is the case in the Solen,
or animal of the Razor-shell ; whose foot is a very powerful boring-
instrument, enabling it to penetrate deeply into the sand. — Here, then,
we have three distinct kinds of ganglionic centres; every one of which
may be doubled, or repeated on the two sides of the body. First, the
cephalic ganglia, a, a, which are probably the sole instruments of sen-
sation and of the consensual movements; as well as of whatever i;o/m7i-
tary power the animal may possess : these are almost invariably
double, being connected together by a transverse band, which arches
over the oesophagus. Second, the pedal ganglion, h, which is usually
single, in conformity with the single character of the organ it supplies;
but in one very rare Bivalve Mollusk, the foot is double, and the
pedal ganglion is double also. Third, the respiratory ganglion, c,
which frequently presents a form that indicates a partial division into
two halves, corresponding with the repetition of the organs it supplies
on the two sides of the body. Besides these principal centres, we
meet with numerous smaller ones upon the nervous cords, (/,/, and

«

NERVOUS SYSTEM OF MOLLUSCA. 485

gi gt) which proceed from them to the different parts of the general
muscular envelop or mantle.

853. Now it will be observed, that the two cephalic ganglia a, a,
are connected with the pedal ganglion 6, by means of a pair of trunks
proceeding from the former to the latter ; and that they are, in like
manner, separately connected with the respiratory or branchial gan-
glion, c. It is found, upon careful dissection, that these cords do not
serve merely to bring the ganglia into relation ; but that a part of
them pass through the ganglion into the trunks proceeding from it.
Thus of the nerves which supply the large fleshy foot, and which
appear to proceed from the pedal ganglion 6, a part are undoubtedly
connected with that ganglion alone, coming into relation with its
vesicular substance ; but a part also pass on to the cephalic ganglia,
by the connecting trunks, — so that these, rather than the pedal gan-
glion, constitute their centre. The same may be said of the nerves
proceeding from the branchial ganglion: a portion of them having
their centre in the vesicular matter of that ganglion ; whilst another
portion has no relation to it whatever (beyond that of proximity), but
passes through or over it, to become connected with the cephalic
ganglia. There is good reason to believe, that the pedal and branchial
ganglia minister to the purely reflex actions of the organs they re-
spectively supply ; and that they would serve this purpose as well, if
altogether cut off from connection with the cephalic ganglia : whilst
the latter, being the instruments of the actions which are called forth
by sensation (whether these be of a consensual or of a voluntary na-
ture), exert a general control and direction over the movements of the
animal.

854. It is difficult to make satisfactory experiments upon this sub-
ject in these animals ; their movements being for the most part slow
and feeble, and their nervous system not readily accessible ; and our
idea of the respective functions of their ganglia is chiefly founded
upon the distribution of their nerves, and upon the analogous opera-
tions of the ganglia that correspond to them in other animals. In
ascending through the series of the Mollusca, we find the Nervous sys-
tem increasing in complexity, in accordance with the general organi-
zation of the body: the addition of new organs of special sensation,
and of new parts to be moved by muscles, involving the addition of
new ganglionic centres, whose functions are especially adapted to
these purposes. But we find no other multiplication of similar cen-
tres, than a doubling on the two sides of the body ; excepting in a
few cases, where the organs they supply are correspondingly multi-
plied. We have a very characteristic example of this in the arms of
the Cuttle-fish, which are furnished with great numbers of contractile
suckers, every one possessing a ganglion of its own. Here we can
trace very clearly the distinction between the reflex actions of each
individual sucker, depending upon the powders of its own ganglion ;
and the consensual or voluntary movement, which results from its
connection with the cephalic ganglia. The nervous trunk, which

486 NERVOUS SYSTEM OF MOLLUSCA.

proceeds to each arm, may be distinctly divided into two tracts; in
one of which there is nothing but fibrous structure, forming a direct
communication between the suckers and the cephalic ganglia ; whilst
in the other are contained the ganglia, which peculiarly appertain to
the suckers, and which are connected with them by distinct filaments:
so that each sucker has a separate relation with a ganglion of its own,
whilst all are alike connected with the cephalic ganglia, and are
placed under their control. We see the results of this arrangement,
in the modes in which the contractile power of the suckers may be
called into operation. When the animal embraces any substance
with its arm (being directed to this action by its sight or other sensa-
tion) it can bring all the suckers simultaneously to bear upon it ; evi-
dently by a voluntary or instinctive impulse, transmitted along the
motor cords, that proceed from the cephalic ganglia to the suckers.
On the other hand, any individual sucker may be made to contract
and attach itself, by placing a substance in contact with it alone ; and
this action will take place equally well, when the arm is separated
from the body, or even in a small piece of the arm when recently
severed from the rest, — thus proving that, when it is directly excited
by an impression made upon itself, it is a reflex act, quite independ-
ent of the cephalic ganglia, not involving sensation, and taking place
through the medium of its own ganglion alone.

855. In the Molluscous classes, generally speaking, the Nervous
system bears but a small proportion to the whole mass of the body;
and the part of it which ministers to the general movements of the
fabric, is often small in proportion to those which serve some special
purpose, such as the actions of respiration. This is what we should
expect from the general inertness of their character, and from the small
amount of muscular structure which they possess. On the other
hand, in the Articulated classes, in which the locomotive apparatus
is highly developed, and its actions of the most energetic kind, we
find the Nervous system almost entirely subservient to this function.
In its usual form, it consists of a chain of ganglia, connected by a
double cord ; commencing in the head, and passing backwards through
the body (Plate II., Fig 2). The ganglia, though they usually appear
single, are really double ; being composed of two equal halves, some-
times closely united on the median line, but occasionally remaining
separate, like the cephalic ganglia of the Solen (Fig. 1, a, a), and
being united together by a transverse commissural trunk. In like
manner, the longitudinal cord, though really double (as seen in the
upper part of Fig. 2), often appears to be single, in consequence of
the close approximation of its lateral halves (as in the lower part of
Fig. 2). In general we find a ganglion in each segment; giving off
nerves to the muscles of the legs, as in Insects, Centipedes, &c. ; or
to the muscles that move the rings of the body, where no extremities
are developed, as in the leech, worm, &c. In the lower Vermiform
(or worm-like) tribes, especially in the marine species, the number of
segments is frequently very great, amounting even to several hundreds;

r

NERVOUS SYSTEM OF ARTICULATA. 487

and the number of ganglia follows the same proportion. Whatever
be their degree of multiplication, they seem but repetitions of one
another ; the functions of each segment being the same with those of
the rest. The cephalic ganglia, however, are always larger and more
important; they are connected with the organs of special sense; and
they evidently possess a power of directing and controlling the move-
ments of the entire body ; whilst the power of each ganglion of the
trunk is confined to its own segment. — The longitudinal ganglionic
cord of Articulata occupies a position, which seems at first sight
altogether different from that of the nervous system of Vertebrated
animals ; being found in the neighbourhood of the ventral or inferior
surface of their bodies; instead of lying just beneath their dorsal or
upper surface. There is reason, however, for regarding the whole
of the body of these animals as having an inverted position ; so that
they maybe considered as really crawling upon their backs. On this
view, their longitudinal nervous tract corresponds with the spinal cord
of . Vertebrata in position^ as we shall find that it does m function.

856. We shall draw our chief illustrations of the structure of the
nervous system in the Articulated series, from the class of Insects; in
which it has been particularly examined. In these animals, the num-
ber of segments never exceeds twelve (exclusive of the head), either
in their larva, pupa, or imago states ; and the total number of pairs of
ganglia, therefore, never exceeds thirteen, including the cephalic
ganglia. These, in the larva, are nearly equal in size, one to another
(Plate II., Fig. 2, a, and 1 — 12); the functions of the different seg-
ments of the body being almost uniform ; and the development of the
organs of special sense not being such, as to involve any considerable
predominance in the size of the cephalic ganglia. We observe, at
the anterior extremity, the pair of cephalic ganglia {a) ; from w^hich
proceeds, on each side, a cord of communication to the first ganglion
(1) of the trunk. This double cord, with the ganglia above and below,
thus forms a ring, which embraces the oesophagus ; the cephalic ganglia
being situated on the upper side of it, whilst the ganglionic column of
the trunk lies beneath the alimentary canal along its whole length.
In the Sphinx ligustri, or Privit Hawk-moth, the nervous system of
whose larva is here represented, the last two segments of the body are
drawn together, as it were, into one; and instead of distinct 11th and
12th ganglia, we find but a single mass, nearly double the size of the
rest, and obviously formed of the elements that would have otherwise
gone to form the two.

857. When the structure of the chain of ganglia is more particularly
inquired into, it is found to consist of two distinct tracts; one of
which is composed of nervous fibres only, and passes backwards from
the cephalic ganglia, over the surface of all the ganglia of the trunk,
giving off branches to the nerves that proceed from them ; whilst the
other includes the ganglia themselves. Hence, as in the Mollusca,
every part of the body has two sets of nervous connections ; one with
the cephalic ganglia; and the other with the ganglion of its own seg-

488

REFLEX ACTIONS OF ARTICULATA.

Fig. 141.

Portion of the ganglionic tract of Poly-
desmus maculatus j—b, inter-gangl ionic
cord; c, anterior nerves; d, posterior
nerves ; /, k, fibres of reflex action ; g, k,
•commissural fibres; i, longitudinal fibres,
softened and enlarged, as they pass
through ganglionic matter.

merit. Impressions made upon the afferent fibres, which proceed
from any part of the body to the cephalic ganglia, become sensations
when conveyed to the latter ; whilst, in respondence to these, the
influence of the instincts, or of the willj operating through the cephalic

ganglia, harmonizes and directs the
general movements of the body, by
means of the efferent nerves proceeding
from them. For the reflex operations,
on the other hand, the ganglia of the
ventral cord are sufficient; each one
ministering to the actions of its own
segment, and, to a certain extent also,
to those of other segments. It has been
ascertained by the careful dissections
of Mr. Newport, that of the fibres con-
stituting the roots, by which the nerves
are implanted in the ganglia, some pass
into the vesicular matter of the gan-
glion, and, after coming into relation
with its vesicular substance, pass out
again on the same side (Fig. 141, y, /c);
whilst a second set, after traversing the
vesicular matter, passes out by the trunks proceeding from the oppo-
site side of the same ganglion ; and a third set runs along the portion
of the cord which connects the ganglia of different segments, and
enters the nervous trunks that issue from them, at a distance of one
or more ganglia above or below. Thus it appears, that an impression
conveyed by an afferent fibre to any ganglion, may excite a motion
in the muscles of the same side of its own segment ; or in those of the
opposite side ; or in those of segments at a greater or less distance,
according to the point at which the efferent fibres leave the cord.

858. The general conformation of Articulated animals, and the ar-
rangement of the parts of their nervous system, render them peculiarly
favourable subjects for the study of the reflex actions ; some of the
principal phenomena of which will now be described. If the head of a
Centipede be cut off, whilst it is in motion, the body will continue to
move onwards by the action of the legs ; and the same w^ill take place
in the separate parts, if the body be divided into several distinct por-
tions. After these actions have come to an end, they maybe excited
again by irritating any part of the nervous centres, or the cut extre-
mity of the nervous cord. The body is moved forwards by the regu-
lar and successive action of the legs, as in the natural state ; but its
movements are always forwards, never backwards, and are only di-
rected to one side, when the forward movement is checked by an
interposed obstacle. Hence, although they might seem to indicate
consciousness and a guiding will, they do not so in reality ; for they
are carried on, as it were, mechanically: and show no direction of ob-
ject, no avoidance of danger. If the body be opposed in its progress

t

I

REFLEX AND CONSENSUAL ACTIONS OF INSECTS. 489

by an obstacle of not more than half its own height, it mounts over
it, and moves directly onwards, as in its natural state ; but if the ob-
stacle be equal to its own height, its progress is arrested, and the cut
extremity of the body remains forced up against the opposing sub-
stance,— the legs still continuing to move. — If, again, the nervous cord
of a Centipede be divided in the middle of the trunk, so that the
hinder legs are cut off from connection with the cephalic ganglia, they
will continue to move, but not in harmony with those of the fore part
of the body; being completely paralyzed, as far as the animal's con-
trolling power is concerned ; though still capable of performing reflex
movements, by the influence of their own ganglia, which may thus
continue to propel the body, in opposition to the determination of the
animal itself. — The case is still more remarkable, when the nervous
cord is not merely divided, but a portion of it is entirely removed
from the middle of the trunk ; for the anterior legs still remain obe-
dient to the animal's control; the legs of the segments, from which
the nervous cord has been removed, are altogether motionless; whilst
those of the posterior segments continue to act, through the reflex
powers of their own ganglia, in a manner which shows that the animal
has no power of checking or directing them.

859. The stimulus to the reflex movements of the legs, in the fore-
going cases, appears to be given by the contact of the extremities with
the solid surface on which they rest. In other cases, the appropriate
impression can only be made by the contact of liquid ; thus a Dytiscus
(a kind of water-beetle), having had its cephalic gjanglia removed,
remained motionless, so long as it rested upon a dry surface ; but when
cast into w^ater, it executed the usual swimming motions with great
energy and rapidity, striking all its comrades to one side by its vio-
lence, and persisting in these for more than half an hour. Other
movements, again, may be excited through the respiratory surface.
Thus, if the head of a Centipede be cut off, and while it remains at
rest, some irritating vapour (such as that of ammonia or muriatic
acid) be caused to enter the air tubes on one side of the trunk, the
body will be immediately bent in the opposite direction, so as to
withdraw itself as much as possible from the influence of the vapour ;
if the same irritation be then applied on the other side, the reverse
movement will take place ; and the body may be caused to bend in
two or three different curves, by bringing the irritating vapour into the
neighbourhood of different parts of either side. This movement is
evidently a reflex one, and serves to withdraw the entrances of the air-
tubes from the source of irritation ; in the same manner as the acts of
coughing and sneezing in the higher animals cause the expulsion, from
the air-passages, of solid, liquid or gaseous irritating matters, which
may have found their way into them.

860. From these and similar facts it appears, that the ordinary
movements of the legs and wings of Articulated animals are of a reflex
nature, and may be effected solely through the ganglia with which
these organs are severally connected ; whilst in the perfect being, they

490 CEPHALIC AND RESPIRATORY GANGLIA OF INSECTS.

are harmonized, controlled, and directed by its instinct or its will,
which act through the cephalic ganglia and the nerves proceeding
from them. There is strong reason to believe, that the operations to
which these ganglia are subservient, are almost entirely of a consensual
nature ; being immediately prompted by sensations, chiefly those of
sight, and seldom involving any processes of a truly rational character.
When we attentively consider the habits of these animals, we find
that their actions, though evidently directed to the attainment of cer-
tain ends, are very far from being of the same spontaneous nature, or
from possessing the same designed adaptation of means to ends, as
those performed by ourselves, or by the more intelligent Vertebrata,
under like circumstances. We judge of this by their unvarying cha-
racter,— the different individuals of the same species executing pre-
cisely the same movements, when the circumstances are the same ; and
by the very elaborate nature of the mental operations, which would be
required, in many instances, to arrive at the same results by an effort
of reason. Of such we cannot have a more remarkable example, than
is to be found in the operations of Bees, Wasps, and other social In-
sects; which construct habitations for themselves, upon a plan which
the most enlightened human intelligence, working according to the
most refined geometrical principles, could not surpass; but which yet
do so without education communicated by their parents, or progressive
attempts of their own, and with no trace of hesitation, confusion, or
interruption, — the different individuals of a community all labouring
effectively for one common purpose, because their instinctive or con-
sensual impulses are the same.

861. It is interesting to remark that, in the change from the Larva
to the perfect or Imago state of the Insect, the Cephalic ganglia
undergo a great increase in size. (Plate II., Fig. 3, a, a.) This
evidently has reference to the increased development of the organs of
special sense in the latter ; the eyes being much more perfectly formed ;
antennae and other appendages used for feeling being evolved ; and
rudimentary organs of hearing and smell being added. In respondence
to the new sensations, which the animal will thus acquire, a great
number of new instinctive actions are manifested ; indeed, it may be
said, that the instincts of the perfect Insect have frequently nothing
in common with those of the Larva. The latter have reference to the
acquirement of food ; the former chiefly relate to the acts of reproduc-
tion, and to the provisions requisite for the deposit and protection of
the eggs and the early nutrition of the young. — We find another im-
portant change in the nervous system of the adult or perfect Insect;
namely, the concentration of the ganglionic matter of the ventral cord
in the thoracic region {e,f) ; with the three segments of which, the
three pairs of legs and the two pairs of wings are connected. The
nine segments of the abdomen, in the perfect Insect, give attachment
to no organs of motion, and are seldom themselves very movable ; and
we find that the ganglia which correspond with them have undergone
no increase in size, but have rather diminished, and have sometimes

STOMATO-GASTRIC AND OTHER NERVES OF INVERTEBRATA. 491

almost completely disappeared. Where the last segment, however,
is furnished with a particularly movable appendage, such as a sting,
or an ovipositor, we always find a large ganglion in connection
wdth it.

862. These ganglia of the ventral cord evidently correspond in
function with the pedal ganglion of the Mollusca ; being so many
repetitions of it ; in accordance with the number of members. We
have now to speak of a system of respiratory ganglia, which also are
repeated in like manner, in accordance with the condition of the respi-
ratory apparatus ; this being diffused through the whole body, in most
of the Articulata, instead of being restricted to one spot as in the
Mollusca. The system of respiratory nerves consists of a chain of
minute ganglia, lying upon the larger cord, and sending off its delicate
nerves between those that proceed from the ganglia of the latter, as
seen in Fig. 2. These respiratory ganglia and their nerves are best
seen in the thoracic portion of the cord, where the cords of communi-
cation between the pedal ganglia diverge or separate from one another.
And this is particularly the case in the Pupa state, when the whole
cord is being shortened, and their divergence is increased. The
thoracic portion of the cord, in the Pupa of the Sphinx ligustri, is
shown in Plate II., Fig. 4; where a, &, and c, represent the 2d, 3d,
and 4th double ganglia of the ventral cord ; c?, c?, the cords of connec-
tion between them, here widely diverging laterally ; and e, e, the small
respiratory ganglia, which are connected with each other by delicate
filaments that pass over the ganglia of the ventral cord, and which
send off lateral branches, that are distributed to the air-tubes and
other parts of the respiratory apparatus, and communicate with those
of the other system.

863. Besides the Respiratory system of ganglia and nerves, there
is in Insects, as in some Mollusks, a set of minute ganglia, which is
especially connected with the acts of mastication and swallowing, its
filaments being distributed to the muscles of the mouth and pharynx,
and some of its ganglia being even found on the stomach, where
that organ is remarkable for its muscular powers. The number and
arrangement of these ganglia vary considerably in different animals,
even in those of the same group ; but some traces of this distinct
system, which is designated as the stomato-gastric, may always be
found. One of the minute ganglia appertaining to it, and forming its
anterior termination, is seen to lie on the median line, in front of the
great cephalic ganglia, in Plate II., Fig. 3, c. From this a trunk
passes backwards along the oesophagus ; which may be likened to the
oesophageal branches of the Par vagum in Vertebrata. Two other
small ganglia, communicating with this, are seen at d, d.

864. We are not without traces, moreover, among Invertebrated
animals, of the Sympathetic system of the higher classes ; though it is
quite a mistake to compare the entire system of nerves and ganglia in
the former, with the Sympathetic system of the latter, — as was for-
merly done. The chief distribution of the branches of the Sympa-

492 NERVOUS SYSTEM OF VERTEBRATA.

thetic of Vertebrata is upon the walls of the blood-vessels, and upon
the muscular substance of the heart and alimentary canal; and it is by
the passage of some of the filaments, from the system of minute
ganglia just pointed out, to the dorsal vessel, that we recognize it as
combining the functions of the Sympathetic with those of the gastric
and cardiac portions of the Par vagum. It will be remembered that
there is a frequent inosculation between these two nerves, even in the
highest animals.

865. Thus we have seen that, in Invertebrated animals, the Nervous
System consists of a series of isolated ganglia, connected together by
fibrous trunks. The number of these ganglia, and the variety of their
function, entirely depend upon the number and variety of the organs
to be supplied. In the lowest Mollusca, the regulation of the ingress
and egress of water seems almost the only function to be performed ;
and here we have but a single ganglion. In the Star-fish, we have
five or more ganglia ; but they are all repetitions, one of another. In
the higher Mollusca, and in Articulata, we have a ganglion, or more
commonly a pair of ganglia, situated at the anterior extremity of the
body, connected with the organs of special sensation, and evidently
exerting a dominant influence over the rest. In the lower Mollusca,
we have but a single ganglion for general locomotion ; but this is
doubled laterally, and repeated longitudinally in the Articulata, in
accordance with the multiplication of their locomotive organs, so as to
form the ventral cord. In like manner, the Mollusca possess a single
ganglionic centre for the respiratory movements; and this is repeated
in every segment of the Articulata, forming a chain of respiratory
ganglia, which regulates the actions of the extensively-diffused respi-
ratory apparatus of these animals. The acts of mastication and deglu-
tition, again, in both sub-kingdoms, are under the control of a distinct
set of ganglionic centres ; which are connected, however, like the
preceding, with the cephalic ganglia ; and it is probable that, as in
other cases, some filaments from the latter enter into all the branches,
which they transmit to the muscles. And we have further seen, that,
wherever special organs are developed, whose operations depend
upon muscular contraction, ganglionic centres are developed in
immediate relation with them ; so as to enable them to act by their
simple reflex power, as well as under the direction of the cephalic
ganglia ; — as in the case of the suckers of the Cuttle-fish.

866. When we direct our attention to the Nervous system of the
Vertebrated series, we perceive that it diflfers from that of the Inver-
tebrated classes we have been considering in two remarkable fea-
tures. In these last, it has seemed but as a mere appendage to the
rest of the system, designed to bring its several parts into more advan-
tageous relation. On the other hand, in the Vertebrata, the whole
structure appears subservient to it, and designed but to carry its pur-
poses into operation. Again, in the Invertebrata, we do not find any
special adaptation of the organs of support for the protection of the
Nervous System. It is either enclosed, with the other soft parts of

I

NERVOUS SYSTEM OF VERTEBRATA. 493

the body, in one general hard tegument, as in the Star-fish and other
Echinodermata, and in Insects, Crustacea, and other Articulata ; or
it receives a still more imperfect protection, or even none at all, as
in the Mollusca. Now in the Vertebrata, we find a special and com-
plex bony apparatus, adapted in the most perfect manner for the pro-
tection of the Nervous system ; and it is, in fact, the possession of a
jointed spinal column, and of its cranial expansion, which best cha-
racterizes the group.

867. The Nervous System of Vertebrata is not merely remarkable
for its high development, relatively to the remainder of the structure.
It is also distinguished by the possession of parts, to which we have
nothing analogous in the lower tribes ; and by the mode in which
these are concentrated and combined, so as to form one continuous
mass, instead of consisting of a series of scattered ganglia. — The
chief parts which are newly introduced (so to speak) in this sub-
kingdom, are the Cerebral Hemispheres and Cerebellum ; of which
there are no traces whatever in the lower Articulata and Mollusca,
and but very minute representations in the highest. These are super-
imposed, as it were, upon the cephalic ganglia connected with the
organs of special sense, and upon the cords that connect them with
the first ganglion of the trunk. — Again we find that the locomotive
ganglia, which formed the long-knotted cord of the Articulata, are
united with the centres of the respiratory system, and with those of
the stomato-gastric system ; to form one continuous tract, which com-
mences anteriorly from the ganglia of special sense, and runs back-
wards* without interruption, in the canal of the Vertebral column,
forming the Spinal Cord. This is a continuous instead of an inter-
rupted ganglionic mass ; it is composed of two lateral halves, precisely
similar to each other; and each of these consists of two parts, as dis-
tinct from each other as the two tracts in the ventral cord of the Arti-
culata,— namely, a fibrous structure, which is continuous between the
Encephalon (or collection of nervous masses within the cranium) and
certain fibres of the roots of the spinal nerves, and which also serves
to connect together the diflferent parts of the cord itself, — and a vesi-
cular portion, which forms the proper centre of another set of fibres
entering into the roots of those nerves. The anterior portion of the
Spinal cord, which is prolonged into the cranium, and comes into
immediate relation with the encephalon, is termed the Medulla Ob-
longata. It is in this that the centres of the respiratory and stomato-
gastric nerves are found ; the situation of these important ganglia
within the cranium, being obviously destined to protect them from
those injuries to which the Spinal Cord itself is liable.

868. Thus, then, we recognize in the Nervous system of Vertebrata
the following fundamental parts. — 1. A system of ganglia subservient
to the reflex actions of the organs of locomotion, and corresponding

* When we speak of the Vertebrata generally, their bodies are of course supposed
to be in a horizontal position, — not vertical as in Man.

494 NERVOUS CENTRES OF FISHES.

with the chain of pedal or locomotive ganglia that makes up the chief
part of the ventral cord of the Articulata ; in this system, the gray or
vesicular matter forms one continuous tract, which occupies the inte-
rior of the Spinal Cord. — 2. A ganglionic centre for the movements
of respiration^ and another for those of mastication and deglutition;
these, with part of the preceding, make up the proper substance of
the Medulla Oblongata. — 3. A series of ganglia, in immediate con-
nection with the organs of ♦§)eaflZ Sense; these are situated within the
cranium, at the anterior extremity of the Medulla Oblongata; and, in
the lowest Vertebrata, they constitute by far the largest portion of the
entire Encephalon. — 4. The Cerebellum, which is a sort of off- shot
from the upper extremity of the Medulla Oblongata, lying behind the
preceding. — 5. The Cerebral Hemispheres, a pair of ganglionic masses,
which lie upon the ganglia of special sense, capping them over more
or less completely, according to their relative development. — These
two last organs exist in the lowest Vertebrata, as in Invertebrated
animals generally, in quite a rudimentary state ; but their develop-
ment, relatively to other parts of the Encephalon, and to the entire
bulk of the animal, increases as we ascend the scale ; so that in Man
and the higher Mammalia they constitute by far the largest portion of
the Nervous centres, and are essential to the greater part of the ope-
rations of the Nervous system. The development of the Cerebral
Hemispheres holds a close relation with the increase of the Intelli-
gence, and with the predominance of the Will over the involuntary
impulses. The increased size of the Cerebellum, on the other hand,
seems connected with the necessity which exists, for the adjustment
and combination of the locomotive powers, when the variety in the
movements performed by the animal is great, and a more perfect
harmony is required among them. — A sketch of the mode in which
these different parts are combined and arranged in the several
classes of Vertebrata, and of their relative development in each,
will aid us in the subsequent more detailed examination of their
functions.

869. In the class of Fishes, taken as a whole, the Encephalon bears
a much smaller proportion to the Spinal Cord, than in the higher
Vertebrata. In the curious Amphioxus, or Lancelot, there is no dis-
coverable nervous mass anterior to the Medulla Oblongata ; and we
have here, therefore, an animal regularly formed upon the plan, which
occasionally presents itself as a monstrosity in Man, namely, having
the Spinal Cord and Medulla Oblongata for the whole of the nervous
centres, and being anencephalous, or destitute of any proper ence-
phalon. In some of the lowest Vermiform (worm-like) Fishes, such
as the Lamprey, the cephalic masses are very little more developed
in proportion to the Spinal Cord, than are the cephalic ganglia of
Insects in reference to their chain of ventral ganglia. But as the
organs of special sense acquire a more complete evolution, we find
the ganglia connected with them presenting a greatly-increased size.
On opening the cranial cavity of a Fish, we usually observe four

ENCEPHALON OF FISHES AND OF HUMAN EMBRYO. 495

nervous masses (three of them in pairs) lying, one in front of the
other, nearly in the same line with the Spinal cord. The first or most
anterior of these are the Olfactory ganglia (Plate II., Figs. 5, 6, 7, a),
or the ganglia of the nerves of smell ; the nature of which is known,
from their being situated at the origin of the Olfactory nerves. In the
Shark and some other Fishes, these are separated from the rest by
peduncles or foot-stalks ; a fact of much interest, as explaining the
arrangement which we find in Man. What is commonly termed the
trunk of his Olfactive nerve is really the commissure connecting the
Qlfactive ganglion, — known as the bulbous enlargement that lies
upon the cribriform plate of the Ethmoid bone, — with the other por-
tions of his Encephalon ; the proper fibres of the nerve being those,
which come off from this ganglion, in the numerous branches that
proceed from it into the nasal cavity. — Behind the Olfactive ganglia
is a pair of masses, 6, 6, of which the relative size varies greatly in
different Fishes. Thus in the Perch, whose Encephalon is here
figured, their size is intermediate between that of the first and third
pairs; being as much inferior to that of the third, as it is superior to
that of the first. On the other hand, in the Shark and several other
Fishes, they are considerably larger than the succeeding pair. These
second ganglia are the Cerebral Hemispheres. — Behind them, and
forming the third pair of ganglionic masses, c, c, are two large bodies,
from which the optic nerves arise ; these are evidently the Optic
ganglia, corresponding to the principal mass of the cephalic ganglia
in Insects, and the higher Mollusca. — And at the back of these, over-
lying the top of the spinal cord, is a single mass, d^ the Cerebellum.
This, also, varies greatly in its relative dimensions; being much more
highly developed in the Active and rapacious Sharks, than it is in
Fishes of inferior muscular energy and variety of movement. — The
Spinal Cord e, is divided at the top by a fissure, w^hich is most wide
and deep beneath the cerebellum, where there is a complete sepa-
ration between its two halves. This opening corresponds to that,
through which the oesophagus passes in the Invertebrata ; but as the
entire nervous mass of Vertebrated animals lies above the alimentary
canal (or nearer the dorsal surface), it does not serve the same pur-
pose in them ; and in the higher classes, the fissure is almost entirely
closed by the union of the two halves on the median plane, — the
fourth ventricle, however, being a remnant of it. This cavity is
partly seen in Fig. 7, which is a vertical section of the brain whose
upper and under surfaces are shown in Figs. 5 and 6.

870. The Optic lobes of Fishes must not be confounded with the
Thalami optici of the higher Vertebrata, with which they have only a
slight analogy, as is proved by their position and connections. They
are rather to be compared with the Corpora Quadrigemina, which are
the real ganglia of the optic nerve. Their analogy is not so complete,
however, to these bodies in their fully-formed brain of the higher
Vertebrata ; as to the certain parts which occupy their place at an
earlier period. In the Human embryo, at about the 6th week, the

496 NERVOUS SYSTEM OF FISHES AND REPTILES.

Encephalon consists of a series of vesicles arranged in a line with
each other; of which those that represent the cerebrum (6, Fig. 14^)
are the smallest, whilst that which represents the cerebellum {d) is
the largest. Between the cerebral and cerebellic vesicles, are two

others, (c, and a), of which the pos-
terior one is the Optic ganglion, and
answers to the Tubercula quadrige-
mina ; whilst the anterior contains
the third ventricle, and corresponds
in some degree to the thalami optici.
This condition is precisely represent-
ed in the Lamprey ; but in most
Fishes, the Optic ganglia, and the
parts surrounding the third ventricle,
form but one lobe ; so that the third
ventricle seems hollowed out of the
optic ganglia, as shown in Fig. 7, c
(Plate II.).— Besides the Olfactive
Human embryo of sixth week, enlarged and Ontip cranD-lia there are in manv

about three time8:-a, vesicle of corpSra ^V , ^P"^_ gf "g'^'^J ^"*^I ^^ '^^^ "^ "»^."J

quadrigemina; 6, vesicle of cerebral hemi- FlshcS dlstinCt Audltory ganglia,

spheres; c. vesicle of ihalami optici and third ^ i • i .1 ^i < • • i.

ventricle; ««, vesicle for cerebellum and me- irom WhlCh thC nCrVCS that minister

dullaoblongaia;e, auditory vesicle;/, olfac- . .v c«:.ncp c\f ViPnrino- nrimnnfp •

tory fossa; A, liver; ** caudal extremity. tO the SenSC 01 Hearing OriginaiC ,

these are frequently blended, how-
ever, with the Medulla oblongata, their vesicular substance forming
a part of its gray matter. — It is curious to notice the very large com-
parative size of the Pineal gland (/*), and of the Pituitary body (A),
in this class ; the functions of these organs are entirely unknown.

871. The Encephalon oi Reptiles does not show any considerable
advance in its general structure, above that of the higher Fishes. The
Cerebral Hemispheres (Figs. 8, 9, 10, h) are always much larger than
the Olfactive and Optic ganglia ; and they generally cover in the
latter (c, e) in part, by their posterior extremities. The Cerebellum is
almost invariably of small proportional dimensions ; and this is espe-
cially the case in the Frog, in which it does not even cover in the
fourth ventricle. This low development of the Cerebellum in Rep-
tiles, is what might be anticipated from the general inertness of these
animals, and the want of variety in their movements. The Spinal
Cord is still very large, in proportion to the nervous masses contained
in the skull ; and, as we shall hereafter see, its power of keeping up
the movements of the body, after it has been cut off from all connec-
tion with the brain, is very considerable. — We find that, in Reptiles,
as in Fishes, the Spinal Cord may have a nearly uniform size from
one extremity to the other, like the ventral cord of the lower Articu-
lata ; or it may present considerable enlargements at particular spots,
like the ganglionic cord in the thoracic region of Insects. This dif-
ference depends upon the degree of development of the special loco-
motive organs. Thus in the Eel and Serpent, whose movements are
accomplished by the undulations of the entire trunk, and which are

NERVOUS CENTRES OF BIRDS AND MAMMALS. 497

destitute of members, we find an uniform development of ganglionic
matter in the spinal cord. On the other hand, in the Flying-fish, in
which the pectoral fins or anterior extremities effect the greater part
of the propulsion of the body, we find a great ganglionic enlargement
of the Spinal cord, at the part with which the nerves of those mem-
bers are connected : in the Frog, whose movements are chiefly
effected by the posterior extremities, we find a similar enlargement at
the roots of the crural nerves ; and in the Turtles and Lizards, the
two pairs of whose members are nearly equal in function, and serve
to effect the principal movements of the body, we find an anterior and
posterior enlargement of the Spinal Cord, corresponding to the parts
with which the nerves of these members are connected.

872. We find in Birds a considerable advance in the character of
the Encephalon, towards that which it presents in Mammalia. The
Cerebral Hemispheres (Plate II., Figs. 11, 12, 13, b) are greatly in-
creased in size ; and then cover in, not merely the olfactory ganglia,
but in great part also the optic ganglia. The former are of compara-

ttively small size ; the organ of smell in Birds not being much deve-
loped. The latter are very large, in conformity with the acuteness
of sight, which is highly characteristic of the class. The Cerebellum
is of large size, as we should expect from the number and complexity
of the muscular movements performed by animals of this class ; but
it is still undivided into hemispheres. The Spinal Cord is still of
considerable size in comparison with the Encephalon ; and it is much
enlarged at the points whence the legs and wings originate. In the
species which have the most energetic flight, such as the Swallow,
the enlargement is the greatest where the nerves of the wings come
off; but in those which, like the Ostrich, move principally by running
on the ground, the posterior enlargement, from which the legs are
supplied with nerves, is much the more considerable.

873. In the Mammalia we find the size and general development
of the Encephalon presenting a gradual increase, as we ascend the
series, from the non-placental Monotremes and Marsupials, towards
Man. In the former, the Hemispheres exhibit no convolutions; and
the great transverse commissure, or connecting band of fibrous struc-
ture,— termed the corpus callosum, — is deficient. As we rise through
the true viviparous division of the class, w^e notice a gradually in-
creasing prolongation of the Cerebral Hemispheres backwards; so
that first the optic ganglia, and then the cerebellum, are covered in
by them. The latter partly shows itself, however, in all but Man and
the Quadrumana, when we look at the brain from above downwards ;
as we see in the Encephalon of the Sheep (Plate II., Figs. 14, 15, d).
The Cerebral hemispheres increase, not only in size, but also in
complexity of structure, both external and internal. Their exterior,
instead of remaining smooth, is marked by convolutions ; which serve
to extend very greatly the amount of surface, over which blood-ves-
sels can pass into the gray substance. Their internal structure be-
comes more complex, in the same proportion as their size and the

32

498 NERVOUS CENTRES OF MAMMALIA.— SPINAL CORD.

depth of their convolutions increase ; and in Man all these conditions
present themselves in a far higher degree than in any other animal.
The number of commissural bands, connecting the two hemispheres
with each other transversely, and uniting their anterior and posterior
portions, is very greatly increased ; and, in fact, a large proportion of
their mass is composed, in Man and the higher Mammalia, of fibres
of this character. In proportion to the increase of the Cerebral hemi-
spheres, there is a diminution in the size of the ganglia of special
sense ; and this is seen when we compare them, not merely with the
rest of the Encephalon, but even with the Spinal Cord. The Olfac-
tive ganglia (Fig. 14, a), are always readily discoverable ; being
separated from the remainder of the encephalic masses by a peduncle
on each side. The Optic ganglia, (Fig. 15, c,) on the other hand,
are so completely covered in by the Hemispheres, that it is only
when the latter are turned aside that we can discern them. They
differ in external aspect from the optic ganglia of Birds and the lower
Vertebrata ; being divided by a transverse furrow into anterior and
posterior eminences, — whence they are known as the Corpora Quad-
rigemina. The Cerebellum is chiefly remarkable for the develop-
ment of its lateral parts or hemispheres, and for the intricate arrange-
ment of the gray and white matter in them (Fig. 15, d) ; the central
portion, sometimes called the vermiform process, is relatively less
developed than in the lower Vertebrata, where it forms the entire
organ. The Spinal Cord is much reduced in size, when compared
with other parts of the nervous centres ; the motions of the animal,
in this class, being more dependent upon its will, or guided by its
sensations ; and the simply reflex actions bearing a much smaller pro-
portion to the rest. The development of ganglionic enlargements, in
accordance with the presence or absence of high locomotive powers
in the extremities, follows the same rule as in the preceding classes.

3. Functions of the Spinal Cord and its JVerves.

874. In commencing our more detailed examination into the func-
tions of the different parts of the Nervous system in Vertebrated
animals, it seems best to commence with the Spinal Cord ; this being
the portion whose presence is most essential to the continuance of
life. As already mentioned. Infants are sometimes born without any
Cerebrum or Cerebellum ; and such have existed for several hours or
even days, breathing, crying, sucking, and performing various other
movements. The Cerebrum and Cerebellum have been experiment-
ally removed from Birds and young Mammalia, thus reducing these
beings to a similar condition ; and all their vital operations have,
nevertheless, been so regularly performed, as to enable them to live
for weeks, or even months. In the Amphioxus, as already remarked,
we have an example of a completely-formed adult animal; in which
no rudiment of a Cerebrum or Cerebellum can be detected. And in
ordinary profound sleep, or in apoplexy, the functions of these or-

REFLEX ACTIONS OF SPINAL SYSTEM. 499

gans are so completely suspended, that the animal is, in all essential
particulars, in the same condition for a time as if destitute of them.
It is possible, indeed, to reduce a Vertebrated animal to the condition
(so far as its nervous system is concerned) of an Ascidian MoUusk
(§ 850); for it may continue to exist for some time, when not merely
the Cerebum and Cerebellum have been removed from above, but
when nearly the whole Spinal Cord has been removed from below,
— that part only of the latter being left, which is the centre of the
respiratory actions, and which corresponds to the single ganglion of
the Tunicata. On the other hand, no animal can exist by its En-
cephalon alone, the Spinal Cord being destroyed or removed ; for
the reflex actions of the latter are so essential to the continuance of
its respiration, and consequently of its circulation, that if they be sus-
pended (by the destruction of the portion of the cord which is con-
cerned in them), all the organic functions must soon cease.

875. Although the Spinal Cord was formerly regarded as little else
than a bundle of nerves proceeding from the Brain, yet its true rank,
as a distinct centre of nervous action, is now universally admitted.
That the actions performed by it are of a purely reflex nature, — con-
sisting in the excitement of muscular movements, in respondence to
external impressions, without the necessary intervention of sensation,
— appears to be a necessary inference, from the facts that have been
brought to light by experiment and observation. Experiments on
the nature of this function are best made upon cold-blooded animals ;
as their general functions are less disturbed by the effects of severe
injuries of the nervous system, than those of Birds and Mammals.
When the Cerebrum has been removed, or its functions have been
suspended by a severe blow upon the head, a variety of motions may
be excited by their appropriate stimuli. Thus, if the edge of the eye-
lid be touched with a straw, the lid immediately closes. If a candle
be brought near the eye, the pupil contracts. If liquid be poured into
the mouth, or a solid substance be pushed within the grasp of the
muscles of deglutition, it is swallowed. If the foot be pinched, or
burned with a lighted taper, it is withdrawn ; and (if the animal ex-
perimented on be a Frog) the animal will leap away, as if to escape
from the source of irritation. If the cloaca be irritated with a probe,
the hind legs will endeavour to push it away.

876. Now the performance of these, as well as of other movements,
many of them most remarkably adapted to an evident purpose, might
be supposed to indicate, that sensations are called up by the impres-
sions ; and that the animal can not on\y feel ^ but can voluntarily di-
rect its movements, so as to get rid of the irritation which annoys it.
But such an inference would be inconsistent with other facts. — In
the first place, the motions performed by an animal under such
circumstances are never spontaneous, but are always excited by a
stimulus of some kind. Thus, a decapiated Frog, after the first vio-
lent convulsive movements occasioned by the operation have passed
away, remains at rest until it is touched ; and then the leg, or its

500 REFLEX ACTIONS OF SPINAL SYSTEM.

■whole body, may be thrown into sudden action, which immediately
subsides again. In the same manner, the act of swallowing is not
performed, except when it is excited by the contact of food or liquor;
and even the respiratory movements, spontaneous as they seem to be,
would not continue, unless they were continually re-excited by the
presence of venous blood in the vessels. These movements are all
necessarily linked with the stimulus that excites them ; — that is, the
same stimulus wull always produce the same movement, when the
condition of the body is the same. Hence it is evident, that the judg-
ment and will are not concerned in producing them ; and that the
adaptiveness of the movements is no proof of the existence of con-
sciousness and discrimination in the being that executes them, — the
adaptation being made for the being, by the peculiar structure of its
nervous apparatus, which causes a certain movement to be executed
in respondence to a given impression, — not by it. An animal thus
circumstanced may be not unaptly compared to an automaton ; in
which particular movements adapted to produce a given effect, are
produced by touching certain springs. Here the adaptation was in
the mind of the maker or designer of the automaton ; and so it evi-
dently is, in regard to the reflex or consensual movements of animals,
as well as with respect to the various operations of their nutritive
system, over which they have no control, yet which concur most ad-
mirably to a common end.

877. Again, we find that such movements may be performed, not
only when the Brain has been removed, the spinal cord remaining
entire, but also when the Spinal cord has been itself cut across, so as
to be divided into two or more portions, — each of them completely
isolated from each other, and from other parts of the nervous centres.
Thus, if the head of a Frog be cut off, and its spinal cord be divided
in the middle of the back, so that its fore legs remain connected with
the upper part, and its hind legs with the lower, each pair of members
may be excited to movement by a stimulus applied to itself; but the
two pairs will not exhibit any consentaneous motions, as they will do
when the spinal cord is undivided. Or, if the Spinal cord be cut
across, without the removal of the Brain, the lower limbs may be
excited to movement, by an appropriate stimulus, though they are
completely paralyzed to the will ; whilst the upper remain under the
control of the animal, as completely as before. Now it is not con-
ceivable that, in this last case, sensation and volition should exist in
that portion of the spinal cord which remains connected with the
nerves of the posterior extremities, but which is cut off from the brain.
For, if it were so, there must be two distinct centres in the same ani-
mal, the attributes of the brain not being affected ; and, by dividing
the spinal cord into two or more segments, we might thus create in
the body of one animal two or more distinct centres of sensation,
independent of that which still holds its proper place in the Encepha-
lon. To say that two or more distinct centres of sensation are pre-
sent in such a case, would really be in effect the same as saying, that

REFLEX ACTIONS OF SPINAL SYSTEM. 501

there are two or more distinct minds in one body, — which is mani-
festly absurd.

878. But the best proofs of the limitation of the endowments of the
Spinal Cord, are derived from the phenomena presented by the Human
subject, in cases where that organ has suffered injury, by disease or
accident, in the middle of the back. We find that, when this injury
has been severe enough to produce the effect of a complete division
of the Cord, there is not only a total want of voluntary control over
the lower extremities, but a complete absence of sensation also, — the
individual not being in the least conscious of any impression made
upon them. When the lower segment of the Cord remains sound,
and its nervous connections with the limbs are unimpaired, distinct
reflex movements may be excited in the limbs by stimuli, directly
applied to them, — as, for instance, by pinching the skin, tickling the
sole of the foot, or applying a hot plate to its surface ; — and this with-
out the least sensation, on the part of the patient, either of the cause
of the movement, or of the movement itself. This fact, taken in
connection with the preceding experiments, both upon Vertebrated
and Articulated animals, distinctly proves that Sensation is not a
necessary link in the chain of reflex actions ; but that all which is
required is an afferent fibre, capable of receiving the impression made
upon the surface, and of conveying it to the centre ; a ganglionic cen-
tre, composed of vesicular nervous substance, into which the afferent
fibre passes ; and an efferent fibre, capable of transmitting the motor
impulse, from the ganglionic centre, to the muscle which is to be
thrown into contraction.

879. These conditions are realized in the Spinal Cord. We may
have reflex actions excited through any one isolated segment of it, as
through a single ganglion of the ventral cord of Articulata ; but they
are then confined to the parts supplied by the nerves of that segment.
Thus, if the spinal cord of a Frog be divided just above the origin
of the crural nerves, the hind-legs may be thrown into reflex contrac-
tion by various stimuli applied to themselves ; but the fore legs will
exhibit no movement of this kind. But when the brain has been
removed, and the Spinal Cord is left entire, movements may be excited
in distant parts, — as, for example, in the fore legs, by any power-
ful irritation of the posterior extremities, — and vice versa. This is
particularly well seen in the convulsive movements, which take place
in certain disordered states of the nervous system ; a slight local irrita-
tion being sufficient to throw almost any muscles of the body into a
state of energetic action (§ 885). And a similar state may be arti-
ficially induced, by applying Strychnine (in solution) to the Spinal
Cord of a decapitated Frog.

880. The minute Anatomy of the Spinal Cord is a subject of great
diflficulty ; and our notions of the course of the fibres within it are
rather founded upon physiological phenomena, and upon the more
evident structure of the ventral column in Articulata, than upon what
can be clearly demonstrated in Vertebrated animals. The roots of

502

FUNCTIONS OP ROOTS OF SPINAL NERVES.

the Spinal nerves are all distinctly separable into an interior and a
posterior fasciculus ; and it is certain that these fasciculi have entirely
opposite functions. If they be laid bare, and the anterior fasciculus
of any spinal nerve be touched, violent contractions are immediately
seen in the muscles supplied by that nerve ; these contractions are as
strongly manifested, if the anterior roots be be divided, and their sepa-
rated ends be irritated ; whilst no such result follows, whatever amount
of irritation be applied to the ends still in connection with the cord.

Notwithstanding these violent
movements, the animal shows lit-
tle or no sign of pain. — On the
other hand, if the posterior roots
be irritated, the animal gives signs
of acute pain, and no vigorous mus-
cular contractions are produced.
The movements which are witness-
ed are evidently of a reflex nature,
being called forth through the ante-
rior roots; as is proved by their
cessation when these are divided.
Further, if the posterior roots be
divided, and the separated ends be
irritated, no effect whatever is pro-
duced ; no movement is excited ;
and no sensation is occasioned ; but
if the ends still in connection with
the cord be irritated, the animal
shows signs of pain as before. —
Hence it is evident, that the poste-
rior roots are made up of efferent
fibres ; that is, of the fibres which
convey impressions towards the
nervous centres: which impressions, if confined to the cord itself,
excite reflex actions; whilst, if conveyed to the brain, they produce
sensations. On the other hand it is equally evident, that the anterior
roots are composed of efferent or motor fibres, which serve to convey
to the muscles the motor impulses originating in the nervous centres ;
these impulses may be occasioned by the reflex action of the Spinal
cord ; or they may descend from the Brain, where they have been
generated by an act of the will. In the accompanying Diagram, the
left side shows the supposed composition of the posterior roots of the
nerves; and the right side, that of the anterior,

881. The Spinal Cord is a completely double tract ; being composed
of two distinct halves, united together on the median plane by nume-
rous commissural fibres. This union is much closer in Man and the
Mammalia than it is in the lower Vertebrata; but the division is still
marked externally, by a deep fissure on the anterior surface of the cord,
and by a shallower one on its posterior aspect. Its surface is traversed,

Diagram of the origins and terminations of
the different groups of nervous fibres:— a, a,
vesicular substance of the spinal cord; &, 6, b,
vesicular substance of the brain ; e, vesicular
substance at the commencement of afferent
nerve, which consists of ci, the cerebral divi-
sion, or sensory nerve passing on to the brain,
and si, the spinal division, or excitor nerve,
which terminates in the vesicular substance of
the spinal cord ; on the other side we have the
efferent or motor nerve proceeding to the mus-
cle rf, likewise consisting of two divisions. —
c3, the cerebral portion, proceeding from, the
brain, and conveying the influence of the will
or of instinct ; and 52, the spinal division, con-
veying the reflex power of the spinal cord.

STRUCTURE OF THE SPINAL CORD. 503

moreover, by two furrows on each side ; so that each half is divided
into three columns, the anterior^ lateral, and posterior. The anterior
roots of the spinal nerves join the Cord for the most part along the
line of the anterior furrow; and the posterior along the line of the
posterior furrow; so that the middle or lateral column lies between
them, the anterior column being altogether in front of them, and the
posterior column behind them. When a transverse section of the
Cord is made, it is seen to contain, on each side, a crescentic patch of
gray or vesicular substance ; the points of each crescent are directed
towards the anterior and posterior furrows of its own side respectively ;
whilst the convexities of the two crescents approach one another near
the median plane, and are connected by a transverse tract of gray matter.
The remainder of the cord is made up of white or tubular substance,
the course of whose fibres is, for the most part, longitudinal. — The pos-
terior peak of the crescentic patch of gray matter approaches very
closely to the bottom of the posterior furrow ; whilst the anterior peak
does not come into nearly the same degree of proximity wuth the bot-
tom of the anterior furrow. Hence it is considered by some, that the
lateral or middle columns of the cord, being much less completely
isolated from the anterior columns than they are from the posterior,
should be associated with the former, under the name of antero-lateral
columns.

882. Upon tracing the roots of the nerves into the substance of the
Cord, the connection of a part of their fibres with its gray or vesicular
substance is easily made evident. Of these fibres, therefore, it serves
as the proper ganglionic centre. There is reason to believe, both from
anatomical investigation, and from physiological phenomena, that, as
in the Articulata, (§ 857,) a part of the afferent or excitor fibres, after
traversing the gray substance, pass out on the same side as the efferent
or motor; whilst another portion crosses to the opposite side, and forms
part of its efferent trunks. The continuity of other fibres, however,
with the longitudinal fibres that form the white strands of the Spinal
Cord, has not been yet clearly demonstrated ; though the analogy of
the ventral cord in Articulated animals, and the physiological pheno-
mena, which show the direct connection between the sensory surfaces
and the brain on the one hand, and between the brain and the mus-
cles on the other, would seem to indicate that such continuity must
exist.— The relative proportions of the gray and white matter in the
Spinal Cord differ considerably at its different parts. Thus in the
cervical region, there is an enlargement corresponding with the origins
of the nerves that form the brachial plexus; this enlargement is partly
caused by an increase in the amount of gray matter; but the whole of
the cervical portion of the cord contains a very large amount of fibrous
structure also. On the other hand, there is a still greater enlargement
of the cord in the lumbar region, at the part whence the nerves of the
lower extremities arise ; and this enlargement is caused by the great
increase in the amount of the gray matter at that point ; the white or
fibrous portion constituting but a comparatively small part of it. Now

504 REFLEX FUNCTION OF THE SPINAL CORD.

these anatomical facts harmonize well with the physiological views
just given; for the actions of the lower extremities being much more
of a simply reflex nature than those of the upper, we find the gangli-
onic portion of the spinal cord exhibiting a corresponding increase at
the origins of their nerves; whilst the actions of the superior extremi-
ties being for the most part of a voluntary character, we find that the
cord mainly consists, at the part with which their nerves are connect-
ed, of white fibrous structure, which appears to convey to those nerves
the direct influence of the brain.

883. It was supposed by Sir C. Bell (who was the first to deter-
mine the relative functions of the two roots of the spinal nerves in
Vertebrated animals), that the anterior columns of the Spinal cord
have a function corresponding to that of the anterior roots of the spi-
nal nerves; and the posterior columns with the posterior roots. But
from the difl5culty of tracing the connection between the longitudinal
fibres of the cord and any portion of the roots, it is at present impos-
sible to say how far there is any anatomical reason for the assumption
of this correspondence ; and it is quite certain, that the physiological
facts at present known, from observation of the effects of disease or
injury upon different tracts of the spinal cord, do not bear out the
supposition. As to what the precise functions of the several columns
are, however, it is not easy to form any other conjecture, that shall
be consistent with all the phenomena at present known.

884. Of the particular Reflex actions to which the Spinal Cord
(using that term in its limited sense, as excluding the Medulla Oblon-
gata) is subservient, those most connected with the organic functions
have already been noticed. They are chiefly of an expulsive kind ;
being destined to force out the contents of various cavities of the body.
Thus the ordinary acts of defecation and urination, the ejaculatio se-
minis, and parturition, are all reflex actions, over which the will has a
greater or less degree of control ; being able to keep the two former
ones in check, so long as the stimulus is not very violent, and being
also capable of effecting them by itself; but having no control over
the two latter, either by way of acceleration or prevention, when once
the stimulus by which they are excited has come into full action. — The
movements of the posterior extremities are among the most remarkable
of those, which seem due to the action of the proper Spinal Cord. It
has been already noticed, that these may be excited, even in Man,
when the spinal cord has been severed in the middle without injury to
its lower segment ; and it is remarkable, that gentle stimuli, applied
to the skin of the sole of the foot, appear the most capable of producing
them. We have seen how completely, in the lower animals, the acts
of progression maybe sustained, by the repeated stimulus of the con-
tact of the ground, or of fluid, without any influence from the cephalic
ganglia ; the power of these being limited, it would seem, to the con-
trol and direction of them. And there is strong reason to believe
that, so far as the ordinary acts of locomotion are concerned, the
movements of the inferior extremities in Man may be performed on the

ACTS OF LOCOMOTION.— CONVULSIVE DISORDERS. 505

same plan, being continued by reflex power, when once set in action
by the will, whilst we are walking steadily onwards, — the mind being
at the same time occupied by some train of thought which engrosses
its whole attention. There are few persons to whom it has not occa-
sionally happened that, on awaking (as it were) from their revery,
they have found themselves in a place very different from that to
which they had intended going ; and even when the mind is sufficient-
ly on the alert to guide, direct, and control the motions of the limbs,
their separate actions appear to be performed without any direct agency
of the will. It is certain that, in Birds, the movements of flight may
be performed after the removal of the Cerebrum.

885. There are many irregular or abnormal reflex actions, performed
through the instrumentality of the Spinal Cord, the study of which is
of the highest importance to the Medical Man. It is probable that
all Convulsive movements are produced through its agency and that of
the Medulla Oblongata ; for it has been found, by repeated experiments,
that these movements are never produced by injuries of the Cerebral
hemispheres. — Convulsive movements may be of three kinds. 1. They
may be simply reflex; being the natural result of some extraordinary
irritation. 2. They may be simply centric ; depending upon a pecu-
liar condition of the ganglionic centre of the Spinal Cord, which oc-
casions muscular movements without any stimulation. 3. They may
depend upon the combined action of both principles; the nervous cen-
tres being in a very irritable state, which causes very slight irritations
(such as would otherwise be inoperative) to excite violent reflex or
convulsive movements. This last is by far the most common cause of
the convulsive actions, that occur in various diseased conditions of the
system. Thus, convulsions are not unfrequent in children, during the
period of teething; being produced by the irritation which results
from the pressure of the tooth as it rises against the unyielding gum.
In this case, the stimulus would scarcely be sufficient to produce the
violent result, were it not for a peculiarly excitable state of the Spinal
Cord, brought about by various causes. In like manner, when such
an excitable state exists, convulsions may be occasioned by the pre-
sence of intestinal worms, of irritating substances, or even simply of
undigested matters in the alimentary canal ; and will cease as soon
as they are cleared out — in the same manner as the convulsions of
teething may often be at once checked — by the free lancing of the
gums.

886. The' influence of the condition of the Spinal Cord itself is
peculiarly seen in the convulsive diseases termed Hydrophobia, Te-
tanus, Epilepsy, and Hysteria. In the first of these, not only the
Spinal Cord, but the Medulla Oblongata, and the ganglia of Special
Sense, are involved ; their peculiar condition being the result, it
would appear, of the introduction of a poison into the blood. It is
most remarkable that the Brain should so completely escape its in-
fluence. When the state of intense excitability in these centres is
once established, the slightest stimulus is sufficient to bring about

506 PECULIARITIES OF CERTAIN SPINAL NERVES.

convulsive movements of the utmost violence. It is characteristic
of this complaint, that the stimuli most effectual in exciting the
movements, are those which act through the nerves of special sense ;
thus the sight or the sound of water will bring on the paroxysm ; and
any attempt to taste it increases the severity of the convulsions. —
In Tetanus there appears to be a similarly excitable state of the
Spinal Cord and Medulla Oblongata, not involving the ganglia of
special sense. This may be the result of causes altogether internal,
as in the idiopathic form of the disease ; in which the condition ex-
actly resembles that which may be artificially induced by the admin-
istration of Strychnine, or by its application to the cord. Or it may
be first occasioned by some local irritation, as that of a lacerated
wound ; the irritation of the injured nerve being propagated to the
nervous centres, and establishing the excitable state in them. When
the complaint has once established itself, the removal of the original
cause of irritation (as by the amputation of the injured limb) is sel-
dom of any avail ; since the slightest impressions upon almost any
part of the body, are suflficient to excite the tetanic spasm. — In like
manner. Epilepsy, which consists in convulsive actions with tem-
porary suspension of the functions of the brain, may result from the
irritation of local causes, like the convulsions of teething; and may,
like them, cease when the sources of irritation are removed. But
when it becomes confirmed, it seems to involve a disorder of the
nervous centres, which no local treatment can influence.

887. These and other forms of Convulsive disorder, when produc-
tive of a fatal result, usually act by suspending the respiratory move-
ments ; the muscles which effect these being fixed by the spasms, so
that the air cannot pass either in or out, and suffocation takes place
as completely as if the entrance to the air-passages were closed. It
is remarkable that every one of them may be imitated by Hysteria; a
state of the nervous system in which there is a peculiar excitability,
but in which there is no such fixed tendency to irregular action as
would indicate any positive disease, — one form of convulsion often
taking the place of another, at short intervals, with the most wonder-
ful variety. It will often be found, that the convulsions may be im-
mediately traced to some local irritation ; thus they are particularly
liable to occur at the catamenial periods, especially if the menstrual
flux be deficient. But the liability to them, resulting from the pecu-
liar excitability of the nervous system, can only be treated by such
constitutional remedies as tend to increase its vigour and to promote
its normal activity.

888. The statement that the spinal nerves arise by double roots, is
not without exception as regards some, which arise from its cranial
prolongation, and which are distributed to the parts of the head and
neck. Th.^ first spinal nerve, ov sub-occipital^ (the 10th pair of Wil-
lis,) not unfrequently arises by a single set of roots, from the anterior
portion of the cord ; and it is then purely motor except in virtue of
its inosculation with other nerves. The Hypoglossal (9th pair of

STRUCTURE OF THE MEDULLA OBLONGATA. 507

Willis) appears to be also a purely motor nerve ; arising by one set
of roots; and being distributed entirely to the muscles of the tongue ;
which organ derives its sensibility from other nerves. The Glosso-
pharyngeal usually arises from a single set of roots, and these corre-
spond with the posterior roots of the spinal nerves ; in some animals,
however, and occasionally in man, there is a distinct anterior root,
and the nerve acquires direct motor functions. It may in some re-
spects be considered as making up, with the preceding, an ordinary
spinal nerve. The Spinal Accessory, again, appears to be chiefly or
entirely a motor nerve at its origin ; and in like manner the Pneumo-
gastric, or Par Vagum, seems at its roots to correspond with the pos-
terior roots of the ordinary spinal nerves, and to execute functions
analogous to theirs ; but these two nerves exchange fibres, so that
each acquires in part the endowments of the other. The Facial nerve,
(or portio dura of the 7th,) which is the nerve that supplies the mus-
cles of the head in general, arises by a single root, and is exclusively
motor in its properties. — except in branches which have received
sensory filaments by inosculation with other nerves. The same is
the case, also, with the Motor JVerves of the Orbit, (the 6th, 4th and
3d, of Willis,) which arise by single roots, and which have no sen-
sory endowments but those which they obtain by inosculation with
the Fifth pair. — On the other hand, the Fifth pair arises by a double
root ; that which corresponds to the anterior or motor root to the spi-
nal nerves is very small, however, and only enters the third division
of the nerve, which supplies the muscles concerned in mastication ;
the other root, corresponding with the posterior roots of the spinal
nerves, is of large size, and its branches are distributed to the face and
head, supplying them with sensibility. Thus the sensory division of
the fifth pair being distributed, not merely to the same parts with its
motor division but also to the parts which derive their motor endow-
ments from the Facial nerve, and from the nerves of the orbit, may
be regarded as making up, together with all of them, one ordinary
Spinal nerve.

4. Functions of the Medulla Oblongata,

889. This portion of the nervous centres, as already stated, does
not differ in any essential particular from the Spinal Cord, of which
it may be considered as a cranial prolongation. But the arrangement
of its constituent parts is peculiar ; being the medium by which the
various strands of the Spinal Cord are connected with the different
portions of the Encephalon : and it is also remarkable as being the
ganglionic centre, concerned in the maintenance of the action of re-
spiration, and in the ingestion of food. Four principal tracts of nerv-
ous matter may be distinguished in each of its lateral halves. These
are, anteriorly, the anterior pyramids ; next, the olivary bodies; next,
the restiform bodies; and, lastly, the posterior pyramids. The fol-
lowing are the principal connections of these different strands, with

508 STRUCTURE AND FUNCTIONS OF MEDULLA OBLONGATA.

the several parts of the Encephalon above, and of the Spinal Cord
below.

890. The Anterior Pyramids, "which consist entirely of fibrous
structure, may be said to connect the motor fibres of the Cerebral
Hemispheres with the antero-lateral columns of the Spinal Cord. Of
the fibres of which they are composed, a large part decussate ; those
that proceed from the right hemisphere, passing into the left side of
the cord ; and those from the left hemisphere into the right side of
the cord, — an arrangement which fully explains the fact, that in Hemi-
plegia, the paralytic aflfection of the body is on the opposite side to
that of the face, the latter corresponding with the side of the brain in
which the disease may exist. A small proportion of the fibres of the
anterior pyramids does not decussate ; and this passes down, with
fibres from the olivary columns, into the anterior columns of the cord ;
whilst the decussating fibres dip more deeply away from the anterior
surface of the cord, and connect themselves rather with its middle
columns.

891. The Olivary bodies are composed externally of fibrous struc-
ture; their fibres being connected above with the Cerebral Hemi-
spheres and Corpora Quadrigemina; and below with the antero-lateral
columns of the Spinal Cord. But beneath the fibrous layer we find
a large mass of vesicular matter, the presence of which gives to the
Medulla Oblongata its ganglionic character. This seems to be the
centre of the respiratory nerves ; it is continuous with the gray matter
of the Spinal Cord below, and with that of certain parts of the Ence-
phalon above ; and, from its peculiar aspect, it is known as the corpus
dentatum.

892. The Restiform columns are continuous above with the fibres
of the hemispheres of the Cerebellum ; and below they pass, without
decussation, chiefly into the posterior columns of the spinal cord, — a
band of «rcz/brm fibres, however, crossing over to the anterior columns
on each side.

893. The Posterior Pyramids are two small strands of fibrous
structure, lying between the two restiform bodies ; and occupying the
portion of the Medulla Oblongata on either side of the posterior
median furrow. They seem to stop short at the fourth Ventricle ;
and it has not yet been ascertained whether they have any connec-
tion with the higher parts of the Encephalon. Below, they assist in
forming the posterior columns of the Spinal Cord ; and, if it be true
that they have no connection with the brain, we may assign to them
the function of connecting the diflferent segments of the cord with each
other.

894. The functions of the Medulla Oblongata are, therefore, of a
double character; — to bring the higher parts of the Encephalon into
connection with the Spinal Cord and the Nerves that issue from it ;
— and to serve as a centre for the reflex movements, performed
through the nerves that issue from it. In both respects it corresponds
precisely with any segment of the Spinal Cord itself; and there is no

REFLEX ACTIONS OF MEDULLA OBLONGATA. 509

reason to believe, that it possesses any other or more special endow-
ments. The importance, however, of the reflex acts of Respiration
and Deglutition, over which it presides, causes this portion of the
Medulla to be the one whose integrity is most essential to the pre-
servation of life ; and therefore it seems to possess a character more
distinctive than it really has.

895. The chief excitor nerve of the respiratory movements, as al-
ready stated (§§ 685-687) is the afferent portion of the Par Vagum;
but the afferent portion of the Fifth pair is also a powerful excitor ;
and the afferent portions of all the spinal nerves, conveying impres-
sions from the general surface of the body, are also capable of con-
tributing to the excitement necessary for the production of the move-
ment.— The chief motor nerves are the phrenic and intercostals ;
which, though issuing from the Cord at a considerable space lower
down, probably originate in the Medulla oblongata. The motor
portions of several other spinal nerves are also partly concerned ; as
are also the Facial nerve, the motor portion of the Par Vagum, and
the Spinal Accessory. The ordinary movements of Respiration
involve little action of any motor nerves but the Phrenic and Inter-
costal ; and it is only when an excess of the stimulus (produced for
example by too long a suspension of the aerating process) excites
extraordinary movements, that the nerves last enumerated are called
into action.

896. The acts o^ Prehension of food with lips, and oi Mastication^
though usually effected by voluntary power in the adult, seem to be
capable of taking place as a part of the reflex operation of the Me-
dulla Oblongata, in the Infant, as in the lower animals. This is
particularly evident in the prehension of the nipple by the lips of the
infant, and the act of suction which the contact of that body (or of
any resembling it) seems to excite. The experiments provided for
us by nature, in the production of anencephalous monstrosities, fully
prove that the integrity of the nervous connection of the lips and
respiratory organs with the Medulla Oblongata, is alone sufficient for
the performance of this action ; and experiments upon young animals,
from which the brain has been removed, establish the same fact.
Thus Mr. Grainger found that, upon introducing his finger, moistened
with milk, or with sugar and water, between the lips of a puppy thus
mutilated, the act of suction was excited ; and not merely the act of
suction itself, but other movements having a relation to it ; for as the
puppy lay on its side, sucking the finger, it pushed out its feet, in
the same manner as young pigs exert theirs in compressing the sow's
dugs. This action seems akin to many of those by which the lower
animals take in their food ; and we may thus recognize in the Medulla
Oblongata a distinct centre of reflex action for the reception and deglu-
tition of aliment, analogous to the stomato- gastric ganglia of Inverte-
brated animals.

897. In the movements o^ Deglutition^ which, as formerly explained,
(§ 453,) are purely reflex, the "chief excitor is undoubtedly the affe-

510 GANGLIA OF SPECIAL SENSE IN MAN.

rent portion of the Glosso-pharyngeal nerve. It is found that, if the
trunk of this nerve, or its pharyngeal (but not its lingual) branches,
be pinched, pricked, or otherwise irritated, whilst still in connection
with the Medulla Oblongata, the movements concerned in the act of
swallowing are excited. The same occurs if, when the trunk of the
Glosso-pharyngeal has been divided, the cut extremity in connection
with the Medulla Oblongata is irritated ; but little or no muscular
contraction is produced by irritation of the separated extremity ;
whence it is apparent, that the Glosso-pharyngeal has little or no di-
rect motor power, but acts as an excitor. In this it appears to be
assisted by the branches of the Fifth pair distributed upon the fauces ;
and probably, also, by the branches of the Superior Laryngeal distri-
buted upon the Pharynx. The motor influence, which is generated
in respondence to the stimulus thus conveyed, appears to act chiefly
through the branches of the Par Vagum, which are distributed to most
of the muscles concerned in swallowing; but the Facial, the Hypo-
glossal, the motor portion of the Fifth, and perhaps also the motor
portions of some of the Cervical nerves, are also concerned in the
movement, and may effect it, though with difficulty, after the pha-
ryngeal branches of the Par Vagum have been divided.

898. In the propulsion of the food down the (Esophagus, to which
the glosso-pharyngeal nerve does not extend, the muscular contrac-
tion, so far as it is of a reflex nature, (§ 455,) must depend upon the
oesophageal branches of the Par Vagum alone ; their afferent portion
being the excitor, and their motor portion givi'ng the requisite stimu-
lus to the muscles. The same must be the case in regard to the mus-
cular contractions of the cardiac and pyloric sphincters, and of the
walls of the stomach, so far as regards their dependence upon the
nervous system at all ; but the degree of this is doubtful.

899. There are other reflex actions of the Medulla oblongata, con-
nected with the regulation of the aperture of the Glottis ; these, which
are effected through the superior and inferior laryngeal branches of
the Par Vagum, will be better noticed when the actions of the La-
rynx are under consideration. — In like manner, the reflex action con-
cerned in the regulation of the aperture of the Pupil will be more
conveniently noticed in the sketch to be presently given of the Physi-
ology of Vision.

5. Functions of the Sensory Ganglia.

900. All the nerves of Sensation, both general and special, may be
traced into a series of ganglionic masses lying at the base of the brain ;
which seem to constitute their own particular centres. Thus we have
seen in Fishes, the Olfactive, Optic, and Auditory ganglia, marked
out as such, by the termination of the nerves proceeding from the
organs of smell, sight, and hearing, in these masses respectively.
These ganglia bear an evident correspondence with the cephalic gan-
glia of the Invertebrata ; which must chiefly, however, be regarded

GANGLIA OF SENSE IN MAN. ' 511

as optic ganglia, since the development of the eyes far surpasses that
of the other organs of special sense. On the other hand, they find
their representatives in certain organs at the base of the brain, in Man
and the higher Mammalia ; which, though small in proportion to the
whole Encephalon, are capable of being clearly marked out, as the
ganglionic centres of the several nerves of sense. Thus, anteriorly,
we have the Olfactive ganglia, in what are commonly termed the bul-
bous expansions of the Olfactive nerve ; which, however, are real
ganglia, containing gray or vesicular substance ; and their separation
from the general mass of the Encephalon, by the peduncles or foot-
stalks commonly termed the trunks of the olfactory nerves, finds its
analogy in many species of Fish (§ 869). The ganglionic nature of
these masses is more evident in many of the lower Mammalia, in
which the organ of smell is highly developed, than it is in Man, whose
olfactive powers are comparatively moderate. — At some distance be-
hind these, we have the representatives of the Optic Ganglia, in the
Tubercula Quadrigemina^ to which the principal part of the roots of
the Optic nerve may be traced. Although these bodies are so small
in Man as to be apparently insignificant, yet they are much larger,
and form a more evidently important part of the Encephalon, in many
of the lower Mammalia ; though still presenting the same general
aspect. — The Auditory ganglia seldom form distinct lobes or projec-
tions ; but are usually lodged in the substance of the Medulla Ob-
longata. Their real character is most evident in certain Fishes, as
the Carp ; in which we find the Auditory Nerve having as distinct a
ganglionic centre as the Optic. In higher animals, however, we are
able to trace the Auditory nerve into a small mass of gray matter,
which lies on each side of the fourth Ventricle ; and although this is
lodged in the midst of parts whose function is altogether diflferent, yet
there seems no reason for doubting that it has a character of its own,
and that it is really the ganglion of the auditory nerve. — We are not
able to fix upon any such mass of gray matter as the distinct Gusta-
tory ganglion ; nor is it necessary to attempt to do so ; for, as we shall
see hereafter, there is strong reason to regard the sense of Taste as
only a refined kind of Touch.

901. At the base of the Cerebral Hemispheres, we find two gan-
glionic masses on either side, through which all the fibres pass that
connect the Hemispheres with the Medulla Oblongata. These are the
Corpora Striata, and Thalami Optici. Upon tracing forwards the tract
of fibres that ascends from the anterior Pyramids, we find it passing
chiefly into the Corpora Striata; whilst, if we follow the Olivary column,
we shall find it to enter the Thalami. The anterior continuations of
these two columns together form the Crura Cerebri, or peduncles of
the Cerebrum ; and the relative functions of the two layers of which
it is composed (which may be very readily isolated) are clearly indi-
cated, by the characters of the nerves that are respectively connected
with them. Thus along the tract that passes from the anterior
Pyramids to the Corpora Striata, we have none but motor nerves ;

512

THALAMI OPTICI, AND CORPORA STRIATA.

Fig. 144.

whilst along the tract that connects the Olivary columns with the
Thalami, there are none but sensory nerves. The fibres of the Crura
Cerebri, after entering these masses, seem to radiate towards all parts

of the surface of the hemi-
spheres, at whose base they
are situated ; but some of them
probably find a ganglionic
centre in these bodies them-
selves ; since their substance
contains a considerable amount
of gray matter. It may be
regarded as not improbable,
then, that we may consider
the Thalami as the ganglionic
centres of common sensation ;
standing in the same relation
to the sensory nerves, that
converge from various parts
of the body towards the En-
cephalon, as do the Optic and
other ganglia to their nerves
of special sensation. And as
these last give origin (as will
be presently shown) to motor
fibres, so may we regard the
ganglionic matter of the Cor-
pora Striata as probably shar-
ing in the same function ; giv-
ing origin to the motor fibres,
which produce the respondent
consensual movements; — ^just
as the anterior peak of gray
matter in the Spinal Cord
gives exit to the motor fila-
ments, which effect the reflex
movements excited through
the afferent fibres that form
part of the posterior roots. —
It must be remembered', how-
ever, that a large proportion
of the fibres, that can be traced from the Medulla Oblongata, through
the Crura Cerebri, into the Thalami Optici and Corpora Striata, pass
through these latter masses, to become continuous with the fibres
radiating from them to the surface of the Cerebral hemispheres. Upon
these, there is no reason to believe that their ganglionic matter exerts
any influence.

902. The functions of this group of ganglia may be partly inferred
from the results of experiments ; and these have been chiefly made

The base of ihe Brain, upon which several sections
have been made, showing the distribution of the diverg-
ing fibres. 1. The medulla oblongata. 2. One-half of
the pons Varolii. 3. The crus cerebri crossed by the
optic nerve (4). and spreading out into the hemisphere
to form the corona radiata. 5. The optic nerve near its
origin. 6. The olfactory nerve. 7. The corpora albi-
cantia. On the right side a portion of the brain has
been removed to show the distribution of the diverging
fibres. 8. The fibres of the corpus pyramidale passing
through the substance of the pons Varolii. 9. The fibres
passing through the thalamus opticus. 10. The fibres
passing through the corpus striatum. 11. Their distri-
bution to the hemispheres. 12. The fifth nerve ; its two
roots may be traced, the one forwards to the fibres of
the corpus pyramidale, the other backwards to the
fasciculi teretes. 13. The fibres of the corpus pyrami-
dale, which pass outwards with the corpus resliforme
into the substance of the cerebellum; these are the arci-
form fibres of Solly. The fibres referred to are those
below the numeral, the numeral itself rests upon the
corpus olivare. 14. A section through one of the hemi
spheres of the cerebellum, showing the corpus rhom-
boideum in the centre of its while substance ; the arbor
vitae is also beautifully seen. 15. The opposite hemi-
sphere of the cerebellum.

FUNCTIONS OF SENSORY GANGLIA. 513

upon the Optic ganglia, or Corpora Quadrigemina. The partial loss
of the ganglion on one side produces temporary blindness in the eye
of the opposite side, and partial loss of muscular power on the oppo-
site side of the body ; and the removal of a larger portion, or the com-
plete extirpation of it, occasions permanent blindness and immobility
of the pupil, and temporary muscular weakness, on the opposite side.
This temporary disorder of the muscular system sometimes manifests
itself in a tendency to move on the axis, as if the animal were giddy ;
and sometimes in irregular convulsive movements. — Here, then, we
have proof of the necessity of the integrity of this ganglionic centre,
for the possession of the sense of vision ; and we have further proof,
that the ganglion is connected with the muscular apparatus, by motor
nerves issuing from it. The reason why the eye of the opposite side
is affected, is to be found in the decussation of the optic nerves; — a
point to be immediately adverted to (§ 910). The influence of the
operation on the muscles of the opposite side of the body, is at once
understood from the fact of the decussation of the motor fibres in the
anterior pyramids (§ 890).

903. Thus we see, that the Optic ganglia receive the impressions
brought from the eyes by the optic nerves, — convert them, as it were
into sensations, — and also transmit motor impulses to the muscular
system, in respondence to those sensations. Thus they have much
analogy to the cephalic ganglia of the lower animals; the greater
part of whose purpose seems to be, to guide the actions of the beings
to which they belong, through the sensations which they receive
(§ 860). But, with a function that is probably the same, there is this
important difference, as to the purpose served by these parts, in the
Encephalon of Man, and of the animals that approach nearest to him
in the conformation of his nervous centres. The Consensual or In-
stinctive movements, which make up nearly the whole of those actions
in the Invertebrata that are not simply reflex, constitute a compara-
tively small proportion of the actions of the higher Vertebrata ; these
being guided in a much greater degree by Intelligence, w^hich reasons
upon the sensations, and devises means to gratify the desires created
by them. Consequently there is reason to think, that the direct ac-
tion of the sensory ganglia upon the muscles is comparatively seldom
exercised, in the active condition of the Cerebrum. There are certain
actions, however, which would seem to take place regularly through
this channel. Thus the consensual movements of the eyes, which
concur to direct their axis towards the same object, appear to depend
upon the impressions made upon the retinae ; for we do not see these
movements taking place with nearly the same exactness in the eyes
of persons who have been born totally blind ; and in those who have
completely lost their sight, after having enjoyed the power of vision,
we may always perceive that, although the two eyes usually move
consentaneously from habit, yet that their axes are parallel, instead
of convergent; so that they do not seem to look at any object, but
beyond it, into vacancy.
33

514 MUSCULAR SENSE.— CONSENSUAL ACTIONS.

904. The existence of a Sensation of some kind, in connection
with a Muscular exertion, seems essential to the continuance of the
latter. Our ordinary movements are guided by what is termed the
Muscular Sense ; that is, by a feeling of the condition of the muscle,
that comes to us through its own sensory nerves. How necessary
this is to the exercise of muscular power, may be best judged of from
cases in which it has been lost. Thus a woman, who had suffered
complete loss of sensation in one arm, but who retained its motor
power, found that she could not support her infant upon it, without
constantly looldng at the child ; and that, if she were to remove her
eyes for a moment, the child would fall, in spite of her knowledge
that her infant was resting upon her arm, and of her desire to sustain
it. Here, the muscular sense being entirely deficient, the sense of
vision supplied what was deficient, so long as it was exercised upon
the object; but as soon as this guiding influence was withdrawn, the
strongest will could not sustain the muscular contraction. — Again, in
the production of vocal sounds, the nice adjustment of the muscles of
the larynx, which is requisite to produce determinate tones, can only
be effected in obedience to a mental conception of the tone to be
uttered ; and this conception cannot be formed, unless the sense of
hearing has previously brought similar tones to the mind. Hence it
is, that persons who are born deaf^ are also dumh. They may have
no malformation of the organs of speech ; but they are incapable of
uttering distinct vocal sounds or musical tones, because they have
not the guiding conception, or recalled sensation, of the nature of
these. By long training, and by efforts directed by the muscular
sense of the larynx itself, some persons thus circumstanced have
acquired the power of speech ; but the want of sufficiently definite
control over the vocal muscles, is always very evident in their use of
the organ.

905. Hence, although the proper consensual actions of Man and of
the higher animals are comparatively few, (the wants which these are
destined to supply in the lower, being in them provided for by the
exercise of intelligence,) we see that not even the proper voluntary
movements can be effected, without the influence of guiding sensa-
tions, felt or conceived. — There are several actions, in regard to
which it does not seem easy to say with certainty, whether they are
of a simply reflex nature, or whether sensation is a necessary link in
the series of changes which they involve. Such are, the act of vom-
iting, produced by various causes that excite nausea, — for example,
by tickling the fauces with a feather ; or the acts of coughing and
sneezing, excited by irritation in the air-passages. In regard to these
last it may be observed, that although the ordinary movements of
Respiration are undoubtedly of a purely reflex character, yet it seems
uncertain, whether those of an extraordinary ndLtnre can be excited by
an impression that is not felt. The act of sneezing is usually excited
by an impression upon the 5th pair; but it may result from the action
of a strong light upon the eyes, and cannot then be excited, unless

CONSENSUAL ACTIONS IN MAN. 515

this produces the sensation of dazzling. — There are numerous cases,
again, in which painful sensations appear to produce or to modify
movement, in a manner that is altogether involuntary. Thus in cases
of excessive irritation of the retina, rendering the eye most painfully
sensitive to even a feeble amount of light, the eyelids are drawn
together spasmodically ; and, if they be forcibly opened, the pupil is
frequently rolled beneath the upper lid, much farther than it could be
carried by a voluntary effort. And in pleuritis, pericarditis, and
other painful affections of the parietes of the chest, we may observe
the usual movements of the ribs to be very much abridged ; and if
the affection be confined to one side, there is a marked curtailment
in its movements, whilst those of the other side may take place as
usual, — a difference which cannot be imitated by a voluntary effort.

i906. Various other facts might be adduced, to show that, in Man,
certain movements are as intimately and necessarily connected with
the excitement of sensations in the sensory ganglia, as others are with
the production of impressions in the ganglia of reflex action. And
it maybe further questioned, in the absence of any precise knowledge
of the subject, w^hether the emotions, when so strongly excited as to
act involuntarily on the body, do not operate through this group of
ganglia and the fibres proceeding from them. There are many ana-
logies between the purely emotional actions of Ma>n, and the instinctive
movements of the lower animals ; each following closely upon sensa-
tions, without any exercise of the reasoning faculty ; and each being
performed, not merely without the mandate of the will, but often m
direct opposition to it. That the Emotions, when they thus affect the
body, do not operate through the same set of nervous fibres as those
which convey the influence of the Will, seems proved by this fa<;t, —
that cases have occurred, in which muscles have been paralyzed to
the Will, whilst they remained obedient to the Emotions; and vi«e
versa. Thus, in one instance, the muscles of one side of the face
were palsied in such a manner, that the individual could not volun^-
tarily close his eye, nor draw his mouth towards that side; yet when
any ludicrous circumstance caused him to laugh, their usual play was
manifested in the expression of his countenance. And in another case,
the muscles were obedient to the will ; but when the individual laiughed
or cried under the influence of an emotion, it was only on one side of
his face. To these may be added another case, in which the right
arm was completely palsied, so that the individual had not the least
voluntary power over it ; yet it was violently agitated, whenever he
met a friend whom he desired to greet.

907. These and similar cases afford sufficient proof, that the direct
influence of the Emotions on the Muscular System operates through
a channel distinct from that, which conveys the influence of the Will ;
and when we consider how closely the Emotions are connected with
the sensations which excite them, and their close analogy with the
instincts of the lower animals, there seems a strong presumption in
favour of the idea, that the motor nerves proceeding from the sensory

516 CONSENSUAL ACTIONS IN MAN.

ganglia constitute their peculiar instrument of operation on the body.
A very characteristic example of the immediate dependence of the
actions of this class upon Sensation, is afforded by the peculiar move-
ments which are excited by the act of tickling. No one can question
the completely involuntary nature of these movements; on the other
hand, they are not reflex^ for they do not take place unless the irrita-
tion is felt. They strictly belong, therefore, to the consensual group
we are at present considering. Now the tickling may produce, not
merely a variety of semi-convulsive movements, tending to withdraw
the body from the source of irritation, but also a tendency to laughter,
and an emotional state connected with it. But it would appear that
the semi-convulsive movements are immediately excited, not by the
emotion, but by the sensation. For there is a great variation amongst
different individuals, as to the results of the irritation; the action of
laughter being excited in some, without any other effect; whilst in
others, spasmodic movements of the extremities take place without
any tendency to laughter, indeed with a feeling of extreme distress.

908. The influence of an excited state of the emotional system of
nerves, is very strongly marked in various disordered states of the
system ; and particularly, as already remarked, in Hydrophobia and
Hysteria (§§886,887). In both these diseases, violent convulsive
paroxysms are brought on, by causes that produce particular sensa-
tions, or emotions consequent upon them. The tendency to imitation
is a most powerful cause in Hysterical subjects; the mere sight of a
paroxysm in one young female, being often sufficient to produce a
similar attack in a whole room-full of her companions. And there are
some persons who possess the powder of commanding an hysterical
paroxysm at will ; not by voluntarily executing the convulsive actions
themselves ; but by " getting up" the particular emotional condition
on W'hich it depends. There can be no doubt that many of the pecu-
liar movements exhibited by the subjects of Mesmeric phenomena,
are the result of a condition of this nature. There appears to be, in
such persons, an excessive activity of the consensual and emotional
system ; so that very slight impressions may produce very powerful
effects ; especially when favoured by the strong desire, on the part of
the patient, to exhibit any peculiar manifestation, that is known to be
expected on the part of the bystanders, — a desire which keeps the
emotional system in a state of tension, and renders it peculiarly respon-
sive to any external influence.

909. Quitting now the functions of the Sensory ganglia, w^e have
briefly to notice certain peculiarities in the characters of the nerves
which issue from them. And of these peculiarities, there is one of a
very remarkable nature, which is common to the three nerves oi special
sense, — namely, the Olfactive, Optic, and Auditory ; — that they are
not in the least degree endowed with common sensibility ; so that they
may be cut, stretched, pinched, &c., without producing the least pain.
Consequently, the ordinary sensibility of the surfaces they supply is
entirelv due to the branches of the Fifth pair, which are distributed

DECUSSATION OF THE OPTIC NERVES. 517

upon them ; and we may have a loss of either the general or the special
sensibility of any of the organs of sense, without the other being
affected, save indirectly. — Again, we do not find that irritation of
these nerves produces any other purely reflex movements, than such
as are connected with the operations of the organs of sense, in which
they respectively originate. Thus the Olfactory nerve cannot, by any
irritation, be made to excite a reflex movement ; the only reflex action
that can be excited by irritating the Optic nerve, is contraction of the
Pupil ; and the regulation of the tension of the Membrana Tympani
(if, as is probable, this is effected by the motor power of the Facial
nerve, excited by impressions made upon the organ of sense,) appears
to be the only reflex action to which the Auditory nerve can mi-
nister.

910. There is a further peculiarity, of a very marked kind, attend-
ing the course of the Optic nerves ; this is the crossing or decussation
which they undergo, more or less Completely, whilst proceeding from
their ganglia to the eyes. In some of the lower animals, in which the
two eyes (from their lateral position) have entirely different spheres of
vision, the decussation is complete ; the whole of the fibres from the
right optic ganglion passing into the left eye, and vice versa. This is
the case, for example, with most of the Osseous Fishes (as the cod,
halibut, &c.) ; and also, in great part at least, with Birds. In the
Human subject, however, and in animals which, like him, have the
two eyes looking in the same direction, the decussation seems less
complete ; but there is a very remarkable arrangement of the fibres,
which seems destined to bring the two eyes into peculianly consenta-
neous action. The posterior border of the optic Chiasma is formed
exclusively oi commissural fibres, which pass from one optic ganglion
to the other, without entering the real optic nerve. Again, the ante-
rior border of the chiasma is composed of fibres, which seem, in like
manner, to act as a commissure between the twore^i??^; passing from
one to the other, without any connection with the optic ganglia. The
tract which lies between the two borders, and occupies the middle of
the chiasma, is the true optic nerve ; and in this it would appear that
a portion of the fibres decussates, whilst another portion passes directly
from each Optic ganglion into the corresponding eye. The fibres
which proceed from the ganglia to the retinae, and constitute the
proper optic nerves., may be distinguished into an internal and an
external tract. Of these, the external, on each side, passes directly
onwards to the eye of that side ; whilst the internal crosses over to
the eye of the opposite side. The distribution of these two sets of
fibres in the retina of each eye respectively, is such that, according
to M. Mayo, the fibres from either optic ganglion will be distributed
toils own side of both eyes; — the right optic ganglion being thus
exclusively connected with the outer part of the retina of the right
eye, and with the inner part of the retina of the left eye ; and the left
optic ganglion being, in like manner, connected exclusively with the
outer side of the left retina, and with the inner side of the right. Now

518 FUNCTIONS OF THE CEREBELLUM.

as either side of the eye receives the images of objects, which are on
the other side of its axis, it follows, if this account of their distribution be
correct, that in Man, as in the lower animals, each ganglion receives
the sensations of objects situated on the opposite sides of the body.
The purpose of this decussation may be, to bring the visual impres-
sions, which are so important in directing the movements of the body,
into proper harmony with the motor apparatus ; so that, the decussa-
tion of the motor fibres in the pyramids being accompanied by a
decussation of the optic nerves, the same effect is produced as if
neither decussated, — which last is the case with Invertebrated ani-
mals in general.

6. Functions of the Cerebellum.

911. Much discussion has taken place, of late years, respecting the
uses of the Cerebellum ; and many experiments have been made to
determine them. That it is in some way connected with the powers
of motion^ might be inferred from its connection with the antero-
lateral columns of the Spinal Cord, as well as with the posterior; and
the comparative size of the organ, in different orders of Vertebrated
animals, gives us some indication of what the nature of its function
may be. For we find its degree of development corresponding pretty
closely with the variety and energy of the muscular movements which
are habitually executed by the species; the organ being the largest
in those animals, which require the combined effort of a great variety
of muscles to maintain their usual position, or to execute their ordi-
nary movements ; whilst it is the smallest in those, which require no
muscular exertion for the one purpose, and little combination of dif-
ferent actions for the "other. Thus in animals that habitually rest and
move upon four legs, there is comparatively little occasion for any
organ to combine and harmonize the actions of their several muscles;
and in these, the Cerebellum is usually small. But among the more
active predaceous Fishes (as the Shark), — Birds of the most pow^erful
and varied flight (as the Swallow), — and such Mammals as can main-
tain the erect position, and can use their extremities for other purposes
than support and motion, — we find the Cerebellum of much greater
size, relatively to the remainder of the Encephalon. There is a
marked advance in this respect, as we ascend through the series of
Quadrumanous animals ; from the Baboons, which usually w^alk on
all-fours, to the semi-erect Apes, which often stand and move on
their hind-legs only. The greatest development of the Cerebellum is
found in Man ; who surpasses all other animals in the number and
variety of the combinations of muscular movement, which his ordi-
nary actions involve, as well as of those which he is capable, by
practice, of learning to execute.

912. From experiments upon all classes of Vertebrated animals, it
has been found that, when the Cerebellum is removed, the power of
walking, springing, flying, standing, or maintaining the equilibrium
of the body, is destroyed. It does not seem that the animal has in

REGULATION OF MOVEMENTS. 519

any degree lost the voluntarypovfer over its individual muscles; but
it cannot combine their actions for any general movements of the body.
The reflex movements, such as those of respiration, remain unim-
paired. When an animal thus mutilated, is laid on its back, it
cannot recover its former posture ; but it moves its limbs, or flutters its
wings, and evidently is not in a state of stupor. When placed in the
erect position, it staggers and falls like a drunken man, — not, however,
without making efforts to maintain its balance. Phrenologists, who
attribute a different function to the Cerebellum, have attempted to put
aside these results, on the ground that the severity of the operation
is alone sufficient to produce them; but as we shall presently see,
many animals may be subjected to a much more severe operation, —
the removal of the Cerebral hemispheres, — without the loss of the
power of combining and harmonizing the muscular actions, provided
the Cerebellum be left uninjured. — Thus, then, the idea of the func-
tions of the Cerebellum, which we derive from Comparative Anatomy,
seems fully borne out by the results of experiment ; and it is also
consistent with the indications, which may be drawn from the obser-
vations of Pathological phenomena. When the Cerebellum is affected
with chronic disease, the motor function is seldom destroyed ; but
the same kind of want of combining power shows itself, as when the
organ has been purposely mutilated. Some kind of lesion of the
motor function is invariably to be observed ; whilst the mental powers
may or may not be affected, — probably according to the influence of
the disease in the Cerebellum upon other parts. The same absence
of any direct connection with the Psychical powers, is shown in the
fact, that inflammation of the membranes covering it, if confined to
the Cerebellum, does not produce delirium. Sudden effusions of
blood into its substance may produce apoplexy or paralysis ; but this
may occur as a consequence of effusions into any part of the Ence-
phalon, and does not indicate, that the Cerebellum has anything to
do with the mental functions, or with the power of the Will over the
muscles.

913. There is another doctrine, however, in regard to the functions
of the Cerebellum, first propounded by Gall; which ought not to be
altogether passed by. According to the system of Phrenologists, the
Cerebellum is the organ of the sexual instinct ; and its connection with
the motor function is limited to the performance of the movements, to
which that instinct leads. This doctrine derives no support, however,
from the facts supplied by Comparative Anatomy ; for there is a com-
plete want of correspondence between the size of the Cerebellum in
different animals, and the power of their sexual instinct. — Again,
although pathology has been appealed to, as showing a decided con-
nection between disease of the Cerebellum and affection of the Genital
organs, (manifesting itself in priapism, turgescence of the testes, seminal
emissions, &c.,) yet it appears, on a careful examination of evidence
that such a sympathy is comparatively rare, not being displayed in
more than one out of every seventeen cases of Cerebellic disease. And

520 SEXUAL INSTINCT.— FUNCTIONS OF THE CEREBRUM.

where it is manifested, it is explicable quite readily by the known
fact that this kind of excitement of the genital organs may be pro-
duced by excitement of the spinal cord and medulla oblongata. — Little
or no light has been thrown on this question by experiment. It was
asserted by Gall, that the Cerebellum is very small in castrated ani-
mals; but this assertion has been met by the most positive counter-
statements on the part of Leuret, who has shown that the average
weight of the Cerebellum (both absolutely, and in proportion to the
weight of the entire encephalon), is even greater in Geldings than in
Stallions or Mares. — It is asserted, however, that the results of ob-
servation in Man lead to a positive conclusion, that the size of the
Cerebellum is a measure of the intensity of the sexual instinct in the
individual. This assertion has been met by the counter-statement of
others, — that no such relation exists. There are, of course, very
great difficulties in regard to the collection of accurate information on
this subject; and the question must be at present regarded as sub
judice.

914. It may be added, that the idea of a special connection between
the sexual instinct and the Cerebellum, is not inconsistent with the
view of its function previously stated ; and it would seem to derive
some confirmation from the fact that an unusual amount of muscular
exertion appears to have a peculiar tendency to depress the sexual
passion even whilst it increases the general vigour of the system. If
the Cerebellum be really connected with both kinds of functions, it
does not seem unlikely that the excessive employment of it upon one,
should diminish its energy in regard to the other. Further, it seems
not improbable that the Lobes of the Cerebellum are the parts spe-
cially concerned in the regulation of the muscular movements ; whilst
the central portion (constituting the Vermiform process in Man, but
forming the entire cerebellum of many of the lower Vertebrata, such
as the Frog), may be the centre of the sexual sensations, and the
instrument of the consensual actions to which they give rise.

7. Functions of the Cerebrum.

915. The view which has been taken of the Comparative structure
of the Nervous system, in different animals, leads to the conclusion,
that the Cerebral hemispheres are far from being the essential parts
of the apparatus they were formerly imagined to be ; and that they are
on the contrary, superadded organs, of which we find no distinct re-
presentatives in the Invertebrata, and of w^hich the first appearance
(in the class of Fishes) exhibits them in the light of appendages, de-
stined to perform some special function peculiar to Vertebrated animals.
The results of the removal of the Cerebral Hemispheres, in animals to
which the shock of the operation does not prove immediately fatal,
fully confirm this view ; and must appear extraordinary to those, who
have been accustomed to regard these organs as the centre of all en-
ergy. Not only Reptiles, but Birds and Mammalia, if their physical

RELATIVE DEVELOPMENT OF THE CEREBRUM. 521

wants be supplied, may survive the removal of the whole Cerebrum
for weeks, or even months. If the entire mass be taken away at once,
the operation is usually fatal ; but if it be removed by successive
slices, the shock is less severe, and the depression it produces in the
organic functions is soon recovered from. It is difficult to substantiate
the existence of actual sensation, in animals thus circumstanced ; but
their movements appear to be of a higher kind than those resulting
from mere reflex action. Thus they will eat food when it is put into
their mouths; although they do not go to seek it. One of the most
remarkable phenomena of such beings, is their power of maintaining
their equilibrium ; which could scarcely exist without consciousness.
If a Rabbit, thus mutilated, be laid upon its back, it rises again ; if
pushed, it walks; if a Bird be thrown into the air, it flies ; if a Frog
be touched, it leaps. If violently aroused, the animal has all the
manner of one waking from sleep ; and it manifests about the same
degree of consciousness as a sleeping Man, whose torpor is not too
profound to prevent his suffering from an uneasy position, and who
moves himself to amend it. In both cases, the movements are con-
sensual only, and do not indicate any voluntary power ; and we may
well believe that, in the former case as in the latter, though felt, they
are not remembered; an active state of the Cerebrum being essential
to memory, though not to sensations, which simply excite certain
actions.

916. As already stated, the relative amount of Intelligence in dif-
ferent animals bears so close a correspondence with the relative size
and development of the Cerebral Hemispheres, that it can scarcely be
questioned that these constitute the organ of the Reasoning faculties,
and issue the mandates by which the Will calls the muscles into
action. It must be borne in mind, however, that size is not by any
means the only indication of their comparative development. As we
advance from the lower to the higher Vertebrata, we observe a marked
advance in the complexity of the structure of the Cerebrum. Its surface
becomes marked by convolutions, that greatly increase the area over
which blood-vessels can enter it from the surrounding membranes ;
and in proportion to the increase in the number and depth of these, do
we find an increase in the thickness of the layer of gray matter, which
is the source of all the powers of the organ. The arrangement of the
white or fibrous tissue, which forms the interior of the mass, also in-
creases in complexity ; and as we ascend even from the lower Mam-
malia up to Man, we trace a marked increase in the number of the
fibres, which establish communications between different parts of the
organ. It is, in fact, not merely from the different parts of the gray
matter, which forms the surface of the hemispheres, that these com-
missural fibres arise ; but also from those isolated portions of vesicular
substance, which are found in different parts of their interior ; and an
extremely complex system is thus formed, which is still but very im-
perfectly understood.

917. The two hemispheres are united on the median line by several

522 COMMISSURES OF THE CEREBRAL HEMISPHERES.

transverse Commissures; of which the Corpus Callosum is the most
important. This consists of a mass of fibres very closely interlaced
together ; which may be traced into the substance of the hemispheres
on each side, particularly at their lower part, where they are connected
with the thalami optici and corpora striata. It is difficult, if not im-
possible, to trace its fibres any further ; but there can be little doubt
that they radiate, with the fibres proceeding from the bodiesjust named,
to the different parts of the surface of the hemispheres. This commis-
sure is altogether absent in Fish, Reptiles, and Birds ; and it is par-
tially or completely wanting in the Mammalia with least perfect
brains, — as the Rodents and Marsupials. — The anterior commissure

Fig. 145.

The mesial surface of a longitudinal section of the brain. The incision has been carried along the
middle line ; between the two hemispheres of the cerebrum, and through the middle of the cerebellum
and medulla oblongata. 1. Tlie inner surface of ihe left hemisphere. 2. The divided surface of the
cerebellum, showing the arbor vitfe. 3. The medulla oblongata. 4. The corpus callosum. curving
downwards in front to terminate at the base of the brain; and rounded behind, to become continuous
with 5, the fornix. 6. One of the crura of the tbrnix descending to 7, one of the corpora albicantia. 8.
The septum lucidum. 9. The velum interpositum, communicating with the pia mater of the convolu-
tions through the fissure of Bicha.t. 10. Section of the middle commissure situated in the third ven-
tricle. 11 "Section of the anterior commissure. 12. Section of the posterior commissure ; the commis-
sure is somewhat above and to the left of the numeral. The interspace between 10 and 11 is the
foramen commune anterius, in which the crus of the fornix (6) is situated. The interspace between 10
and 12 is the foramen commune posterius. 13. The corpora quadrigemina, upon which is seen resting
the pineal gland, 14. 15. The iter a tertio ad quarlum ventriculum, or aqueduct of Sylvius. 16. The
fourth ventricle. 17. The pons Varolii, through which are seen passing the diverging fibres of the
corpora pyramidalia. 18. The crus cerebri of the left side, with the third nerve arising from it. 19.
The tuber cinereum, from which projects the infundibulum, having the pituitary gland appended to its
extremity. 20. One of the optic nerves. 21. The left olfactory nerve terminating anteriorly in a
rounded bulb.

particularly unites the corpora striata of the two sides ; but many of
its fibres pass through those organs, and radiate towards the convolu-
tions of the hemispheres, especially those of the middle lobe. This
commissure is particularly large in those Marsupials, in which the
Corpus Callosum is deficient. — The posterior commissure is a band of
fibres which connects the optic thalami; crossing over from the poste-
rior extremity of one to that of the other. — Besides these, there are
other groups of fibres, which seem to have similar commissural func-
tions, but which are intermingled with vesicular substance. Such are
the soft commissure, which also extends between the thalami ; the
Pons Tarini, which extends between the two crura or peduncles of
the cerebrum ; and the Tuber cinereum, which seems to unite the

FUNCTIONS OF THE CEREBRUM. 523

optic tracts with the thalami, the corpus callosum, the fornix, &c.,
and to be a common point of meeting for several distinct groups of
fibres.

918. The anterior and posterior parts of the hemispheres, more-
over, are connected by Ivngifudinal Commissures; of which some lie
above, and some below, the corpus callosum. Above the transverse
fibres of the corpus callosum, there is a longitudinal tract on each side
of the median line, w^hich serves to connect the convolutions of the
anterior and posterior lobes of the brain. — And above this, again, is
the superior longitudinal commissure, which is formed by the fibrous
matter of the great convolution nearest the median plane on the up-
per surface of the brain, and which connects the convolutions of the
anterior and middle lobe with those of the posterior. — Beneath the
great transverse commissure, we find the most extensive of all the
longitudinal commissures, namely, the fornix. This is connected in
front with the optic thalami, the raammillary bodies, the tuber cine-
reum, &c.; and behind, it spreads its fibres over the hippocampi (major
and minor), which are nothing else than peculiar convolutions that
project into the posterior and descending cornua of the lateral ventri-
cles.— The fourth longitudinal commissure is the tceniasemicircularis,
which forms part of the same system of fibres with the fornix ; con-
necting the corpus mammilare and thalamus opticus with the middle
lobe of the cerebral hemisphere. — If, as Dr. Todd has remarked, we
could take away the corpus callosum, the gray matter of the internal
convolution, and the ventricular prominence of the optic thalami, then
all these commissures falltogether, and become united as one and the
same series of longitudinal fibres.

919. Besides these, it is probable that the different convolutions
have their own commissural fibres uniting them with each other, as
well as their radiating fibres connecting them with the thalami optici
and corpora striata ; but these have not been certainly demonstrated.
It is curious that there should be no direct communication between
the Cerebral hemispheres and the Cerebellum ; the only commissural
band between them being the processus a cerebello ad testes, w^hich
passes onwards, through the tubercula quadrigemina, to the thalamus
opticus on each side. This would seem to confirm the idea of the
complete distinctness of their functions.

920. Very little light can be thrown by experiment upon the func-
tions of the several parts of the Cerebral hemispheres, or of the gan-
glionic masses with w^hich they are so intimately connected. In the
experiments already referred to, in which the hemispheres were en-
tirely removed, slice by slice, it was noticed that injuries of these
organs neither occasion any signs of pain, nor give rise to convulsive
movements. Even the thalami and corpora striata may be wounded,
without the excitement of convulsions ; whilst, if the incisions involve
the tubercula quadrigemina, convulsions uniformly occur. It has been
often observed in Man, that, w^hen it has been necessary to separate
protruded portions of the brain from the healthy part, no sensation

524 SLEEP; COMA.

was produced, even though the mind was perfectly clear at the time.
Hence it would appear that neither is the Cerebrum itself the centre
of sensation, nor is it so connected with that centre, as to be able to
convey to it sensory impressions of an ordinary kind. This is analo-
gous to the condition of tl^e nerves of special sense, as already re-
marked. That no irritation of the cerebral substance should excite
convulsive movements, is a very remarkable circumstance; and it
seems to indicate, that the changes which mental operations produce
in the cerebral fibres, cannot be imitated, as changes in other motor
fibres may be, by physical impressions.

921. There are various conditions, some of them natural, others
morbid, in which the distinctness of the functions of the Cerebral He-
mispheres is well marked. Thus in profound sleep, they seem to be
entirely dormant ; the Spinal system, by which the necessary reflex
actions are carried on, being alone in a state of activity. In this con-
dition, the Sensory ganglia also appear to be in a torpid state ; but in
less profound sleep, actions are often performed, which maybe referred
to the consensual group, — being such as the sensation would imme-
diately prompt, without any reflection, and not being remembered in
the waking state. Thus we turn in our beds, under the influence of
an uneasy sensation ; or we give some sign of recognition when our
names are called. The first of these appears to be a purely consen-
sual movement, being as automatic as if it were a reflex action ; the
other seems to have become as automatic, by the influence of habit,
and to belong to that class, in which the mind was at first involved,
but in which, after very frequent performance, the sensation suggests
the action so immediately and invariably, that the action seems to take
place without any concern on the part of the will. Of these secondary
automatic actions, as they are termed, we have many examples in that
condition, in which the mind, though active, is so completely absorbed
by some train of thought, as to be in a state of revery^ and to be in-
sensible to external objects ; in such a condition, the individual may
continue reading aloud, playing a piece of music, or performing any
other action, in which the muscular movements are immediately
directed by the sensations ; but he cannot carry on two distinct and
independent trains of thought.

922. In the Coma of Apoplexy, Narcotic Poisoning, &c., we wit-
ness the same gradations as in ordinary sleep. When it is least pro-
found, it seems to affect the Cerebral hemispheres alone ; the Sensory
Ganglia being still, in some degree, open to the reception of impres-
sions. When complete, however, none but reflex actions can be
excited ; and if it advance to a fatal termination, it does so by the
supervention of the same state of torpidity in the Medulla Oblongata,
whereby the respiratory movements are brought to a close. These
movements do not cease until the power of deglutition has been lost,
and until the eye ceases to close when the edge of the lid is irritated ;
but when this is the case, a fatal termination may be apprehended, as

SOMNAMBULISM; MEMORY. 525

it is thus shown that the torpor is extending to the Spinal system of
nerves.

923. In the condition of Dreaming, it would seem as if the Cere-
brum were partially active; a train of thought being suggested, fre-
quently by sensations from without ; which is carried on without any
controlling or directing power on the part of the Mind ; and which is
not corrected, or is only modified in a limited degree, by the know-
ledge acquired by experience. This condition is still more remarkable
in Somnambulism, or (as it has been better termed) Sleep- waking ; on
which the dreams are not only aded^ but may be often acted on with
the utmost facility, — a suggestion conveyed through any of the senses
excepting sight (which is usually in abeyance) being apprehended and
followed up with the utmost readiness, and, in like manner, with little
or no correction from experience. Between this condition, and that
of ordinary dreaming, on the one hand, and that of complete insensi-
bility on the other, there is every shade of variety; which is presented
by different individuals, or by the same individuals at different times.
The Cerebellum, in the Sleep-waking state, seems to be frequently in
a condition of peculiar activity; remarkable power of balancing and
combining the movements of the body, being often exhibited.

924. The faculty of Memory appears to be the exclusive attribute
of the Cerebral hemispheres; no impressions made upon the Organs of
Sense being ever remembered, unless they are at once registered (as it
were) in this part of the nervous centres. This faculty is one of those
first awakened in the opening mind of the Infant; and it is one of
which we find traces in animals, that seem to be otherwise governed
by pure Instinct. It obviously affords the first step towards the exer-
cise of the reasoning powers ; since no experience can be obtained
without it; and the foundation of all intelligent adaptation of means
to ends, lies in the application of the knowledge which has been
acquired, and stored up in the mind. There is strong reason to
believe, that no impression of this kind, once made upon the Brain,
is ever entirely lost, — except through disease or accident, which will
frequently destroy the memory altogether, or will annihilate the recol-
lection of some particular class of objects or of words. All memory,
however, seems to depend upon the principle of Association ; one idea
being linked with another, or w^th a particular sensation, in such a
manner as to be called up by its recurrence; and a period of many
years frequently intervening, without the combination of circumstances
presenting itself, which is requisite to arouse the dormant impression
of some early event. Sometimes this combination occurs in dreaming,
delirium, or insanity; and ideas are recalled, of which the mind, in a
state of healthy activity, has no remembrance.

925. Although there does not seem any improbability in the suppo-
sition, that different faculties of the mind should have different parts
of the Cerebral hemispheres as their special instruments, yet suflScient
evidence of the correctness of the (so-called) Phrenological distribu-
tion of organs, has not yet, in the Author's opinion, been adduced, to

526 FUNCTIONS OF THE SYMPATHETIC SYSTEM.

justify its admission into an Elementary Treatise like the present; and
the subject will therefore be passed by.

8. Functions of the Sympathetic System.

926. The Cerebro-Spinal apparatus, of which the several parts have
now been described, is not the only system of ganglia and nerve-
trunks, that is contained within the body of a Vertebrated animal.
There is another system, having its own set of centres, and its own
distribution of branches; characterized also* by a peculiarity in the
nature of the nervous fibres, of which its trunks are composed ; and
communicating at numerous points with the preceding. It will be
remembered that, in front of the vertebral column, there is a series
of ganglia on each side ; communicating, on the one hand, with the
spinal nerves, as they issue from the< vertebral canal; and also con-
necting themselves with the two large semilunar ganglia, which lie
amidst the abdominal viscera ; as well as with a series of ganglia, that
is found near the base of the heart. In the head, also, there are
numerous scattered ganglia, which evidently belong to the same
system; having numerous communications with the cephalic nerves;
and being also connected with the chain of ganglia in the neck. The
branches proceeding from this series of ganglia are distributed, not to
the skin and muscles (like those of the cerebro-spinal system), but to
the organs of digestion and secretion, to the heart and lungs, and
particularly to the walls of the blood-vessels, on which they form a
plexus, whose branches probably accompany their minutest ramifica-
tions. The peculiar connection of this system of nerves with the
organs of vegetative life, has caused it to receive the designation of
the Nervous System of Organic Life ; the Cerebro-Spinal system being
termed the Nervous System of Animal Life. It is also not unfre-
quently termed the ganglionic system; on account of the separation
of its centres into scattered ganglia, which forms a striking contrast
to the concentration that is so evident in the Cerebro-Spinal system.
But this term is objectionable, as leading to a supposed analogy
between this system and the general nervous system of Invertebrata,
whose centres are equally scattered ; — an analogy which is completely
erroneous, since, as we have seen, this last is chiefly the representative
of the Cerebro-Spinal system of Vertebpted animals. The term
Sympathetic is, perhaps, the best; although it must not be supposed
that the system of nerves is the instrument of by any means all the
sympathies, which manifest themselves between different organs.

927. The Sympathetic system contains two classes of nervous
fibres ; — the ordinary white tubular fibres, all of which are probably
derived from the Cerebro-Spinal system ; and the gray or gelatinous
fibres, which seem to belong exclusively to itself (§ 375). True it
is, that some of these last are found in the spinal nerves ; but they
seem, even there, to form part of the Sympathetic system, — their
centres being the ganglia on the posterior roots of the Spinal nerves,

FUNCTIONS OF THE SYMPATHETIC SYSTEM. 527

which communicate with the true Sympathetic ganglia, and which
seem to form a part of the same series. Thus we may consider each
system as intermingling itself with the other; — the Cerebro-spinal
system transmitting some of its fibres, both motor and sensory, into
the Sympathetic ; — whilst the Sympathetic is represented in the Cere-
bro-Spinal system, by certain fibres and collections of vesicular mat-
ter of its own. The trunks that proceed from the Semilunar ganglia,
are almost entirely composed of gray or organic fibres ; whence it is
evident that these ganglia are to be regarded as the true centres of
the Sympathetic system. On the other hand, the trunks which issue
from the chain of spinal ganglia, contain a large admixture of white
or tubular fibres.

928. The Sympathetic nerves possess a certain degree of power of
exciting Muscular contractions, in the various parts to which they
are distributed. Thus by irritating them, immediately after the death
of an animal, contractions may be excited in any part of the aliment-
ary canal, from the pharynx to the rectum, according to the trunks
which are irritated, — in the heart, after its ordinary movements have
ceased, — in the aorta, vena cava, and thoracic duct, — in the ductus
choledochus, uterus, Fallopian tubes, vas deferens, and vesiculee semi-
nales. But the very same contractions may be excited, by irritating
the roots of the Spinal nerves, from w^hich the Sympathetic trunks
receive their white fibres ; and there is, consequently, strong reason
to believe that the motor power of the latter is entirely dependent
upon the Cerebro-spinal system. Whatever sensory endowments the
Sympathetic trunks possess, are probably to be referred to the same
connection. In the ordinary condition of the body, these are not
manifested. The parts exclusively supplied by Sympathetic trunks
do not appear to be in the least degree sensible ; and no sign of pain
is. given, when the Sympathetic trunks themselves are irritated. But
in certain diseased conditions of those organs, violent pains are felt
in them; and these pains can only be produced, through the me-
dium of fibres communicating with the sensorium through the spinal
nerves.

929. It is difficult to speak with any precision, as to the functions
of the Sympathetic system. There is much reason to believe, how-
ever, that it constitutes the channel, through which the passions and
emotions of the mind affect the Organic functions; and this especially
through its power of regulating the calibre of the arteries. We have
examples of the influence of these states upon the Circulation, in the
palpitation of the heart which is produced by an agitated state of
feeling ; in the Syncope, or suspension of the heart's action, which
sometimes comes on from a sudden shock ; in the acts of blushing
and turning pale, which consist in the dilatation or contraction of the
small arteries ; in the sudden increase of the salivary, lachrymal, and
mammary secretions, under the influence of particular states of mind,
which increase is probably due to the temporary dilatation of the ar-
teries that supply the glands, as in the act of blushing ; and in many

528 SENSATION.

other phenomena. It is probable that the Sympathetic system not
only thus brings the Organic functions into relation with the Animal:
but that it also tends to harmonize the former with each other, so as
to bring the various acts of secretion, nutrition, &c., into mutual con-
formity. Of the distinctive function of the gray or organic fibres, we
have no knowledge whatever. Possibly they may have some direct
influence upon the chemical processes, which are involved in these
changes, and may thus affect the quality of the secretions ; whilst the
office of the white fibres is rather to regulate the diameter of the blood-
vessels supplying the glands, and thus to determine the quantity of
their products.

CHAPTER XIII.

OF SENSATION, GENERAL AND SPECIAL.

1 . Of Sensation in general,

930. All beings of a truly Animal Nature possess, there is good
reason to believe, a consciousness of their own existence, first derived
from a feeling of some of the corporeal changes taking place within
themselves ; and also a greater or less amount of sensibility to the
condition of external things. This consciousness of what is taking
place within and around the individual, is all derived from impres-
sions made upon its afferent nervous fibres ; which, being conveyed
by them to the central sensorium^ are \\\exefeU (§ 390). Of the mode
in w^hich the impression, hitherto a change of a physical character, is
there made to act upon the mind^ we are absolutely ignorant ; we only
know the fact. Although we commonly refer our various sensations
to the parts at which the impressions are made, — as, for instance,
when we say that we have a pain in the hand, or an ache in the leg,
— we really use incorrect language ; for though we may refer our
sensations to the parts where the impression is first made on the
nerves, they are really felt in the brain. This is evident from two
facts ; — first, that if the nervous communication between the part and
the brain, be interrupted, no impressions, however violent, can make
themselves felt; and second, that if the trunk of the nerve be irritated
or pinched, anywhere in its course, the pain which is felt is referred,
not to the point injured, but to the surface to which these nerves
are distributed. Hence the well-known fact that, for some time
after the amputation of a limb, the patient feels pains, which he
refers to the fingers or toes that have been removed ; this continues,
until the irritation of the cut extremities of the nervous trunks has
subsided.

SENSATION;— GENERAL AND SPECIAL. 529

931. It would seem probable that, among the lower tribes of Ani-
raals, there exists no other kind of sensibility, than that termed gene-
ral or common; which exists, in a greater or less degree, in every
part of the bodies of the higher. It is by this, that we feel those
impressions, made upon our bodies by the objects around us, which
produce the various modifications of pain^ the sense of contact or
resistance, the sense of variations of temperature, and others of a
similar character. From what w^as formerly stated (§ 403) of the
dependence of the impressibility of the sensory nerves, upon the
activity of the circulation in the neighbourhood of their extremities,
it is obvious that no parts destitute of blood-vessels can receive
such impressions, or (in common language) can possess sensibility.
Accordingly we find that the hair, nails, teeth, cartilages, and other
parts that are altogether extra-vascular, are themselves destitute of
sensibility ; although certain parts connected with them, such as the
bulb of the hair, or the vascular membrane lining the pulp-cavity of
the tooth, may be acutely sensitive. Again, in tendons, ligaments,
fibro-cartilages, bones, &c., whose substance contains very few ves-
sels, there is but a very low amount of sensibility. On the other
hand, the skin and other parts, which are peculiarly adapted to re-
ceive such impressions, are extremely vascular: and it is interesting
to observe, that some of the tissues just mentioned become acutely
sensible, when new vessels form in them in consequence of diseased
action. It does not necessarily follow, however, that parts should be
sensible in a degree proportional 'to the amount of blood they may
contain ; for this blood may be sent to them for other purposes, and
they may contain but a small number of sensory nerves. Thus, it is
a condition necessary to the action of Muscles, that they should be
copiously supplied with blood (§359); but they are by no means
acutely sensible ; and, in like manner. Glands, which receive a large
amount of blood for their peculiar purposes, are far from possessing a
high degree of sensibility.

932. But besides the general, or common sensibility, which is dif-
fused over the greater part of the body, in most animals, there are
certain parts, which are endowed with the property of receiving im-
pressions of a peculiar or special kind, such as sounds or odours, that
would have no influence on the rest ; and the sensations which these
excite, being of a kind very different from those already mentioned,
arouse ideas in our minds, which we should never have gained with-
out them. Thus, although we can acquire a knowledge of the shape
and position of objects by the touch, we could form no notion of their
colour without sight, of their sounds without hearing, or of their
odours without smell. The nerves which convey these special im-
pressions, as already mentioned, are not able to receive those of a
common kind ; thus the eye, however well fitted for seeing, would not
feel the touch of the finger, if it were not supplied by branches from
the 5th pair, as well as by the Optic. Nor can the different nerves of
special sensation be aflfected by impressions, that are adapted to ope-

530 OF SENSATION IN GENERAL.

rate on others ; thus the ear cannot distinguish the slightest difference
between a luminous and a dark object ; nor could the eye distinguish
a sounding body from a silent one, except when the vibrations can be
seen. But Electricity possesses the remarkable power, when trans-
mitted along the several nerves of special sense, of exciting the sen-
sations peculiar to each ; and thus, by proper management, this single
agent may be made to produce flashes of light, distinct sounds, a
phosphoric odour, a peculiar taste, and a pricking feeling, in the same
individual, at one time. Each kind of sensation may also be excited,
however, by mechanical irritation of the nerve which is subservient to
it. — The feeling of pain may be induced by impressions made upon
the nerves of special sense, as well as upon those of feeling ; if these
impressions be too violent or excessive. Thus the dazzling of the
eye by a strong light, and still more, the action of a moderate light in
an irritable state of the retina, — sudden loud sounds, or even sounds
of moderate intensity but of peculiar harshness,— powerful odours,
even such as are agreeable in moderation, — produce feelings of un-
easiness, which may be properly called painful, even though they are
different from those excited through the nerves of common sensation.

933. As a general rule, it may be stated, that the violent excite-
ment oi any sensation is disagreeable; even when the same sensation,
experienced in a moderate degree, may be a source of extreme plea-
sure. But the question of degree is relative^ rather than absolute ;
that is, a sensation may be felt as extremely violent by one individual ;
whilst another, who is more accustomed to sensations of the same
kind, is not disagreeably affected by it. Thus, our sensations of heat
and cold are entirely governed by the previous condition of the parts
affected; as is shown by the well-known experiment, of putting. one
hand in hot water, the other in cold, and then transferring them both
to tepid water, — which will seem coo] to the one hand, and warm to
the other. The same is the case in regard to light and sound, smell
and taste. A person going out of a totally dark room, into one mode-
rately bright, is for the time painfully impressed by the light, but soon
becomes habituated to it; whilst another who enters it from a room
brilliantly illuminated, will consider it dark and gloomy.

934. The intensity with w^hich sensations are felt, therefore, de-
pends upon the degree of change which they produce in the sensorium.
The more frequent the recurrence of any particular sensation, the more
does the system become adapted to it, and the less change does it
produce. It is, therefore, perceived in a less and less degree, and at
last it ceases to excite attention. The stoppage of a constantly-recur-
ring sensation, however, will produce a change, which makes as
strong an impression on the system as its first commencement ; thus
there are persons, who have become so habituated to the sound of a
waterfall or even of a forge-hammer, that they cannot sleep anywhere
but in its vicinity ; and it is well known that, when a person has gone
to sleep under the influence of some continuous or frequently-recur-
ring sound (such as the voice of a reader, the dropping of water, the

r

EFFECTS OF ATTENTION. 531

tread of a sentinel, &c.), the cessation of the sound will cause his
awaking.

935. The acuteness of particular sensations is influenced in a re-
markable degree, by the attention they receive from the mind. If the
mind be entirely inactive, as in profound sleep, no sensation what-
ever is produced by very feeble impressions ; on the other hand, when
the mind is from any cause strongly directed upon them, impressions
very feeble in themselves produce sensations of even painful acute-
ness. It is in this manner, that the habit of attending to sensations
of any particular class, increases their vividness ; so that they are at
once perceived by an individual on the watch for them, when they
do not excite the observation of others. We may even, by a strong
effort, direct the mind into one particular channel, so as to receive
only those sensations which have reference to it, and to be uncon-
scious quoad all others. Thus, the application of the mind to some
particular train of thought may prevent our being conscious of any-
thing that is going around or within us, — the conversation of friends,
— the striking of the clock, — the calls of hunger, &c. This abstrac-
tion may be altogether voluntary ; and the possession of the power of
thus withdrawing the mind at will from the influence of external dis-
turbing causes, and of fixing it upon any particular train of ideas, is
an extremely valuable one. But it may also be involuntary, and may
be a source of inconvenience from its tendency to recur at improper
times, — producing the habitual state which is known as absence of
mind or revery.

936. It is desirable that we should make a distinction, between
the sensations themselves, and the ideas which are the immediate
results of those sensations, when they are perceived by the mind.
These ideas relate to the cause of the sensation, or the object by which
the impression is made. Thus, the formation of the picture of an
object, upon the retina, produces a certain impression upon the optic
nerve ; which being conveyed to the sensorium, excites a correspond-
ing sensation, with which, in all ordinary cases, we immediately con-
nect an idea of the nature of the object. So closely, indeed, is this
idea usually related to the sensation, that we are not in the habit of
making a distinction between them. Thus I may say at this moment,
** I see a book on the table before me ;" the fact being, that I am con-
scious of a certain picture, which conveys to my mind the ideas of a
book and of a table, and of their relative positions ; these ideas being
(in Man) the result of experience and association, — in fact, originating
in the immediate application of the knowledge we have previously
acquired, that a certain object, whose picture we see, is a book, an-
other object a table, and so on. We are liable to be deceived in this
assumption ; as when, by a clever imitation, a picture on a plane
surface is made to represent an object in relief, so perfectly as at
once to excite the idea of the latter, — which may not be corrected,
until we have ascertained by the touch the flatness of the real object.

937. This production of ideas, by the agency of sensations, is a

532 PERCEPTIONS, INTUITIVE AND ACQUIRED.

process altogether mental, and dependent upon the laws of Mind.
We find that some of these perceptions or elementary notions are intui-
tive; that is, they are prior to all experience, and are necessarily con-
nected with the sensation which produces them, as reflex movements
are with the impression that excites them. This seems to be the
case, for example, with regard to erect vision. There is no reason
whatever to think, that either infants or any of the lower animals see
objects in an inverted position, until they have corrected their notion
by the touch ; for there is no reason why the inverted picture on the
retina should give rise to the idea of the inversion of the object. The
picture is so received by the mind, as to convey to us an idea of the
position of external objects, which harmonizes with the ideas we
derive through the touch ; and whilst we are in such complete igno-
rance of the manner in which the mind becomes conscious of the
sensation at all, we need not feel any difficulty about the mode in
which this conformity is effected. But in Man, as already stated, the
attaching definite ideas to certain groups of lines, colours, &c., with
respect to the objects they represent, is a subsequent process, in
which experience and memory are essentially concerned ; as we see
particularly well, in cases presently to be referred to, in which the
sense of sight has been acquired comparatively late in life, and in
which. the mode of using it, and of connecting the sensations received
through it with those received through the touch, has had to be
learned by a long-continued training. The elementary notions thus
formed, — which may, by long habit, present themselves as immedi-
ately and unquestionably, as if they were intuitive, — are termed ac-
quired perceptions.

938. It is probable that, among the lower animals, the proportion
of intuitive perceptions is much greater than in Man ; whilst, on the
other hand, his power of acquiring perceptions is much greater than
theirs. So that, whilst the young of the lower animals very soon
becomes possessed of all the knowledge, which is necessary for the
acquirement of its food, the construction of its habitation, &c., its
range is very limited, and it is incapable of attaching any ideas to a
great variety of objects, of which the Human mind takes cognizance.
This correspondence between the acquired perceptions of Man, and
the intuitive perceptions of many of the lower animals, is strikingly
evident in regard to the power of measuring distance. This is
acquired very gradually by the Human infant, or by a person who has
first obtained the faculty of sight later in life ; but it is obviously pos-
sessed by many of the lower animals, to whose maintenance it is essen-
tial immediately upon their entrance into the world. Thus a Fly-
catcher, immediately after its exit from the egg, has been known to
peck at and capture an insect, — an action which requires a very exact
appreciation of distance, as well as a power of precisely regulating
the muscular movements in accordance with it.

I

SENSE OF TOUCH.— CUTANEOUS PAPILLJE. 533

2. Of the Sense of Touch.

939. By the sense of Touch is usually understood that modification
of the common sensibility of the body of which the surface of the Skin
is the especial seat, but which exists also in some of its internal re-
flexions. In some animals, as in Man, nearly the whole exterior of the
body is endowed with it, in no inconsiderable degree ; whilst in others,
as the greaternumber of Mammalia, most Birds, Reptiles, and Fishes,
and a large proportion of the Invertebrata, the greater part of the body
is so covered with hairs, scales, bony or horny plates, shells of various
kinds, complete horny envelops, &c., as to be nearly insensible; and
the faculty is restricted to particular portions of the surface, or to or-
gans projecting from it, which often possess a peculiarly high degree
of this endowment. Even in Man, the acuteness of the sensibility of
the cutaneous surface varies greatly in different parts ; being greatest
at the extremities of the fingers, and in the lips; and least in the skin
of the trunk, arm, and thigh. Thus the two points of a pair of com-
passes (rendered blunt by bits of cork) can be separately distinguished
by the point of the middle finger, when approximated so closely as one-
third of a line ; whilst they require to be opened so widely as 30 lines
from each other, to be separately distinguished, when pressed upon
the skin over the spine, or upon that of the middle of the arm or
thigh.

940. The impressions that produce the sense of Touch are received
through the sensory papillcB^ with which

the surface of the true Skin is beset, — Fig. i46.

more or less closely according to the part
of it that is examined. These papillse are
minute elevations, which enclose loops of
capillary vessels (Fig. 146), and branches
of the sensory nerves. With regard to the
precise course of the latter, there is some
uncertainty; but it is probable from ana-
logy, that the representation given of

lltel^:*

wmmmm

them by Gerber (Fig. 147), is in the Capillary network at margin of lips.

main correct; and that each loop of the Sen-
sory nerve is surrounded by a small quantity of vesicular matter, on
some change in which the formation of the sensory impression is
immediately dependent. It is peculiar to the sense of Touch, and
to that of taste (which is a modification of it) that the impression
must be made by the contact of the object itself with the sensory
surface and not through any intermediate agency. The only excep-
tion to this is in regard to the sense of Temperature, which seems to
be in many respects different from ordinary touch ; here the proximity
of the warm or cold body is sufficient, — the impressions being made
after the manner of those of odours, sounds, &c. It is worth re-
marking, with reference to the question of the special nature of the

534 CUTANEOUS PAPILLJE.— SENSE OF RESISTANCE.

sensory fibres, which are the channel of these impressions, that no
mechanical irritation of the nerves of common sensation ever seems

Fig. 147.

Distribution of the tactile nerves at the extremity of the human thumb, as seen in a thin perpendicu-
lar section of the skin.

to excite sensations of heat or cold ; these being apparently as distinct
from the sense of contact, as they are from that of light or sound.

941. The only idea communicated to our minds, when this sense is
exercised in its simplest form, is that of resistance; and we cannot acquire
a notion of the size or shape of an object, or of the nature of its sur-
face, through this sense alone, unless we move the object over our own
sensory organ or pass the latter over the former. By the various de-
grees of resistance which we then encounter, we form our estimate of
the hardness or softness of the body. By the impressions made upon
our sensory papillae, when they are passed over its surface, we form
our idea of its smoothness or roughness. But it is through the mus-
cular sense which renders us cognizant of the relative position of the
fingers, the amount of movement the hand has performed in passing
over the object, and of other 'impressions of like nature, that we ac-
quire our notions of the size and figure of the object; and hence we
perceive, that the sense of touch, without the power of giving motion
to the tactile organ, would have been of comparatively little use. It
is chiefly in the variety of movements, of which the hand of Man is
capable, — thus conducive as they are, not merely to his prehensile
powers, but to the exercise of his sensory endowments, — that it is
superior to that of every other animal; and it cannot be doubted, that
this affords us a very important means of acquiring information in re-
gard to the external world, and especially of correcting many vague
and fallacious notions, which we should derive from the sense of Sight,
if used alone. On the other hand, it must be evident that our know-
ledge would have but a very limited range, if this sense were the only
medium, through which we could acquire ideas. Of this we have the
clearest evidence in the very imperfect development of the mental
powers, in those unfortunate persons who have suflfered under the
deprivation of sight and hearing from their birth, and who have been
consequently cut off* from the most direct means of profiting by the
knowledge possessed by their fellow-beings, through want of power
to use the organs of speech. It is only where such individuals have

SENSE OF TEMPERATURE.— NERVES OF TASTE. 535

fallen under the care of judicious and persevering instructors, that
their mental powers have been called into their due activity, or that
any ideas have been awakened, beyond those immediately connected
with the gratification of the animal wants, or with painful or pleasur-
able sensations. Thus a mind, quite capable of being aroused to activ-
ity and enjoyment, may remain in a condition nearly allied to that of
idiocy, simply for want of the sensations requisite to produce ideas of
a higher and more abstract character than those derived through the
senses of Touch, Taste, and Smell.

942. It is not by any means certain, whether the sense of Tempe-
rature is not conveyed by a set of fibres, altogether distinct from those
which minister to the proper sense of Touch or resistance. For many
cases are on record, in which it has been lost, whilst the ordinary
sense of touch remains ; and it is sometimes preserved, when there is a
complete loss of every other kind of sensibility. So again we find
that the subjective sensations of temperature,— ^-that is, sensations which
originate from changes in the body itself, not from external impres-
sions,— are frequently excited quite independently of the tactual sen-
sations ; a person being sensible of heat or of chilliness in some part of
his body, without any real alteration of its temperature, and without
any corresponding affection of the tactual sensations. — It is curious
that the intensity of the sensation of temperature should depend, not
merely upon the relative degree of heat to which the part is exposed
(§ 933), but also upon the extent of the surface over which it is applied;
— a weaker impression made on a larger surface, seeming more power-
ful than a stronger impression made on a small surface. Thus, if the
forefinger of one hand be immersed in water at 104°, and the whole
of the other hand be plunged in water at 102°, the cooler water will
be thought the warmer; whence the well-known fact, that water in
which a finger can be held without discomfort, will produce a scald-
ing sensation when the entire hand is immersed in it.

3. Of the Sense of Taste.

943. The sense of Taste, like that of Touch, is excited by the direct
contact of particular substances with certain parts of the body: but it
is of a much more refined nature than touch ; inasmuch as it commu-
nicates to us a knowledge of properties, which that sense would not
reveal to us. All substances, however, do not make an impression on
the organ of Taste. Some have a strong savour, others a slight one,
and others are altogether insipid. The cause of these differences is
not altogether understood ; but it may be remarked that, in general,
bodies which cannot be dissolved in water, alcohol, &c., and which
thus cannot be presented to the gustative papillse in a state of solution,
have no taste. This sense has for its chief purpose, to direct animals
in their choice of food ; hence its organ is always placed at the en-
trance to the digestive canal. In higher animals, the tongue is the
principal seat of it ; but other parts of the mouth are also capable of

536 NERVES OF TASTE.— COMPOUND NATURE OF THE SENSE.

receiving the impression of certain savours. The mucous membrane

which covers the tongue is copiously supplied with papillae, of various

forms and sizes. Those of simplest structure closely resemble the

cutaneous papillae ; but there are others,
F'gi^a which resemble clusters of such papillae,

each being composed of a fasciculus of
looped capillaries (Fig. 148), and probably
containing a similar fasciculus of nervous
loops, lying in the midst of vesicular mat-
ter. No difference of function has yet
been ascertained to exist among the several
forms of lingual papillae. When the pa-
pillae are called into action by the contact

papilla oFthrrgJa."' '""'''°"" of substances having a strong savour, they

not unfrequently become very turgid, by a

distension of their vessels analogous to that which occurs in erection;

and they rise up from the surface of the mucous membrane, so as to

produce a decided roughness of its surface.

944. There has been much discrepancy of opinion as to the nerve
which is specially concerned in the sense of Taste. The tongue is
supplied by two sensory nerves; the lingual branch of the 5th pair;
and the glosso-pharyngeal. The former chiefly supplies the upper
surface of the front of the tongue, and is copiously distributed to the
papillae near the tip. The latter is mostly distributed upon the mu-
cous surface of the fauces, and upon the back of the tongue ; but it
sends a branch forwards, beneath the lateral margin on each side,
which supplies the edges and inferior surface of the tip of the tongue,
and inosculates with the preceding. There is reason to believe, from
experiment, that the gustative sensibility of the tongue is not destroyed
by section of either of these nerves ; though it is impaired by the
total or partial loss of sensibility over certain parts of the surface.
There seems good reason to conclude, that the lingual branch of the
5th pair is the nerve through which the sense of Taste, as well as
that of Touch, is exercised, in the parts of the tongue to which it is
specially distributed, — which are those that possess both senses in the
most acute degree ; and that the Glosso-pharyngeal is subservient to
the same functions in the parts supplied by it, being probably the
exclusive channel, also, through which the impressions made by
disagreeable substances taken into the mouth are propagated to the
Medulla Oblongata, so as to produce nausea and excite efforts to
vomit. The latter nerve is also, as we have seen, the principal chan-
nel of the impressions, that give rise to the reflex act of swallowing;
with which the 5th pair is concerned in a much inferior degree
(§ 897).

945. A considerable part of the impression produced by many sub-
stances taken into the mouth, is received through the sense of Smell,
rather than through that of Taste. Of this, any one may easily satisfy
himself, by closing the nostrils, and breathing through the mouth only,

CONDITIONS OF THE SENSE OF SMELL.

537

whilst holding in his mouth, or even rubbing between his tongue and
his palate, some aromatic substance ; its taste is then scarcely recog-
nized, although it is immediately perceived when the nasal passages
are reopened, and its effluvia are drawn into them. There are many
substances, however, which have no aromatic or volatile character;
and whose taste, though not in the least dependent upon the action of
the nose, is nevertheless of a powerful character ; but these for the
most part produce, by irritating the mucous membrane, a sense of
pungency^ allied to that which the same substances (acids, for instance,
pepper, or mustard), will produce, when applied to the skin for a suffi-
cient length of time, especially if the Epidermis have been removed.
Such sensations, therefore, are evidently of the same kind with those
of Touch ; differing from them only in the degree of sensibility of the
organ, through which they are received. The sense of Taste, then,
in its ordinary acceptation, may be regarded as a compound of those
of Smell and Touch.

4. Of the Sense of Smell.

946. Certain bodies possess the property of exciting sensations of
a peculiar nature, which cannot be perceived by the organs of taste
or touch, but which seem to depend upon the diffusion of the particles
of the substance through the surrounding air, in a state of extreme
Ininuteness. As the so-
lubility of a substance Tig.u9.
in liquid seems a neces-
sary condition of its ex-
citing the sense of Taste,
so does its volatility, or
tendency to a vaporous
state, appear requisite
for its having Odorous
properties. Most vola-
tile substances are more
or less odorous ; whilst
those which do not
readily transform them-
selves into vapour, usu-
ally possess little or no
fragrance in the liquid
or solid state, but ac-
quire strong odorous
properties, as soon as
they are converted into
vapour, — by the aid of

heat, for example. There are some solid substances, which possess
very strong odorous properties, without losing weight in any appre-
ciable degree by the diffusion of their particles through the air. This

A view of the First pair, or Olfactory Nerves, with the Nasal
Branches of the Fifth pair; 1, frontal sinus; 2, sphenoidal sinus ;
3, hard palate; 4, bulb of olfactory nerve; 5, branches of the
olfactory nerve on the superior and middle turbinated bones ;
6, spheno-palatine nerves from the second branch of the fifth
pair; 7, internal nasal nerve from the first branch of the fifth;
8, branches of 7 to the Schneiderian membrane ; 9, ganglion of
Cloquet in the foramen incisivum; 10, anastomosis of the
branches of the fifth pair on the inferior turbinated bone.

538 CONDITIONS OF THE SENSE OF SMELL.

is the case, for example, with Musk ;^a grain of which has been kept
freely exposed to the air of a room, whose door and windows were
constantly open, for a period often years ; during which time the air,
thus continually changed, was completely impregnated with the odour
of musk; and yet, at the end of that time, the particle was not found
to have perceptibly diminished in weight. We can only attribute
this result to the extreme minuteness of the division of the odorous
particles of this substance. There are other odorous solids, such as
Camphor, which rapidly lose weight by the loss of particles from their
surface, when freely exposed to the air.

947. The conditions of the sense of Smell are very simple. The
Olfactory nerve is minutely distributed over the Schneiderian mem-
brane, which is itself highly vascular. The arrangement of the ulti-
mate fibres of this nerve has not been ascertained. The Schneiderian
membrane is kept constantly but moderately moist, by a mucous se-
cretion from its surface ; and this condition is essential to the acute
perception of odours. If the mucous surface be too dry, as happens
when the 5th pair is paralyzed, the sensation is blunted or even de-
stroyed; and the same effect is produced by the presence of too copious
a secretion, — as when we are suffering under an ordinary cold. — The
highest part of the nasal fossae appears to be that in which there is
the most acute sensibility to odours; and hence it is that, when we
snuff ihe. air, so as to direct it into this portion of the cavity, we per-
ceive delicate odours, which would otherwise have escaped us. The
acuteness of the sense of Smell depends, in no small degree, upon
the extent of surface exposed by the membrane lining the nasal cavi-
ty ; and in this respect, Man is far surpassed by many of the lower
Mammalia, especially the Ruminants, which are warned by its means
of the proximity of their enemies. The habit of attention to sensory
impressions of this class, however, very much heightens their acute-
ness ; hence in those who suffer under blindness and deafness con-
jointly, it is usually the principal means by which individuals are
distinguished, and the presence of strangers recognized ; and there
are cases, in which individuals in a state of Somnambulism have ex-
hibited a degree of acuteness of smell, quite comparable to that which
is characteristic of Deer, Antelopes, &c.

948. Besides ministering to the sense of Smell, by stimulating the
secreting powers of its surface, the 5th pair has another very import-
ant function, — that of endowing the interior of the nose with com-
mon sensibility, and thus receiving the impression produced by acrid
or pungent substances, which act upon it in the same way as they
do upon the tongue. Such substances are felt, by the irritation they
produce, rather than smelt; and the sensation they occasion gives rise
to the consensual act o^ sneezing, by which a violent blast of air is di-
rected through the nasal passages, in such a manner as to clear them
of the irritating matter, whether solid (as snuff), fluid, or gaseous.
Hence this action may be excited by the contact of an irritant with
the Schneiderian membrane, after the olfactory nerve has been di-

SENSE OF HEARING.— ACOUSTIC PRINCIPLES. 539

vided, if the branches of the 5th pair be entire ; whilst it does not
take place when the 5th pair is paralyzed, even though the sense of
smell is retained.

5. Of the Sense of Hearing,

949. By this sense we become acquainted with the sounds pro-
duced by bodies in a certain state of vibration ; the vibrations being
propagated through the surrounding medium, by the corresponding
waves or undulations which they produce in it. Although air is the
usual medium through which sound is propagated, yet liquids or
solids may answer the same purpose. On the other hand, no sound
can be propagated through a perfect vacuum. — It is a fact of much
importance, in regard to the action of the Organ of Hearing, that so-
norous vibrations which have been excited, and are being transmitted,
in a medium of one kind, are not imparted with the same readiness
to others. The following conclusions have been drawn from experi-
mental inquiries on this subject.

I. Vibrations excited in solid bodies, may be transmitted to water
without much loss of their intensity ; although not with the same rea-
diness that they would be communicated to another solid.

II. On the other hand, vibrations excited in water lose something
of their intensity in being propagated to solids; but they are returned,
as it were, by these solids to the liquid, so that the sound is more
loudly heard in the neighbourhood of these bodies, than it would
otherwise have been.

III. The sonorous vibrations are much more weakened in the trans-
mission of solids to air ; and those of air make but little impression on
solids.

IV. Sonorous vibrations in water are transmitted but feebly to air ;
and those which are taking place in air are with difficulty communi-
cated to water ; but the communication is rendered more easy, by the
intervention of a membrane extended between them.

The application of these conclusions, in the Physiology of Hearing,
will be presently apparent.

950. It is on the Auditory nerve (commonly termed the Portio
Mollis of the 7th pair), that the sonorous undulations make their im-
pression; but we invariably find, that this impression is made through
the medium of a liquid, contained in a cavity, on the walls of which
the ultimate branches of this nerve are distributed. The simplest
form of the organ of Hearing, such as we find in some Crustacea and
certain Fishes, consists merely of a cavity excavated in the solid
framework of the head ; which cavity is filled with liquid, and lined
by a membrane on which the auditory nerve is distributed. These
animals are inhabitants of the water ; and the sonorous vibrations
excited in this medium, being communicated to the solid parts of the
head, will be by them again transmitted to the contained fluid, with-
out much diminution of their intensity ; according to principles i. and

540 SIMPLEST FORMS OP THE ORGAN.— TYMPANUM.

n.-— In those Crustacea, however, which chiefly inhabit air, as well
as in the greater number of the class of Fishes, we find the auditory
cavity or vestibule no longer entirely closed ; but having an aperture
on its external side, which is covered in by a membrane. Here the
vibrations of the liquid within the cavity, will be rnore directly excited
by those of the surrounding medium ; for if this be water, it will pro-
pagate its undulations into the cavity, with little interruption from
the membrane stretched across its mouth ; whilst, if it be air, the
interposition of this very membrane will greatly assist in the trans-
mission of the vibrations to the water of the auditory cavity, accord-
ing to principle iv. In most animals, which have the organ of
hearing constructed upon this simple plan, the force of the vibrations
of the fluid within the cavity is increased by several minute stony
concretions (termed otolithes), which are suspended in it. These
act according to principle ii. Some traces of them are found in the
higher animals ; in which they are for the most part superseded, how-
ever, by an apparatus better adapted to augment the intensity of the
sonorous vibrations.

951. This apparatus consists, in all Vertebrated animals above the
inferior Reptiles, of the tympanum or drum, with its membrane and
chain of bones; together with, in the Mammalia, the external ear;
which is adapted to direct itself, more or less completely, towards the
point from which the sonorous vibrations proceed, and to give them a
degree of preliminary concentration. The tympanic apparatus is inter-
posed between the external ear and the membrane covering theybra-
men ovale, which is the entrance to the real auditory cavity ; and its
purpose is evidently to receive the sonorous vibrations from the air,
and to transmit them to that membrane, in such a manner that the
vibrations thus excited in the latter may be much more powerful than
they would be if the air acted immediately upon it, as in the lower
Vertebrata. The usual condition of the Membrana Tympani appears
to be rather lax ; and, when in this condition, it vibrates in accord-
ance with grave or deep tones. By the action of the tensor tympani
it may be tightened, so as to vibrate in accordance with sharper or
higher tones ; but it will then be less able to receive the impressions
of deeper sounds. This state we may easily induce artificially, by
holding the breath, and forcing air from the throat into the Eustachian
tube, so as to make the membrane bulge out by pressure from within ;
or by exhausting the cavity by an effort at inspiration, with the mouth
and nostrils closed, which will cause the membrane to be pressed
inwards by the external air. In either case, the hearing is imme-
diately found to be imperfect; but the deficiency relates only to grave
sounds, acute ones being heard even more plainly than before. There
is a different limit to the acuteness of the sounds, of which the ear
can naturally take cognizance, in diff*erent persons. If the sound be
so high in pitch, that the membrana tympani cannot vibrate in unison
with it, the individual will not hear it, although it may be loud ; and
it has been noticed that certain individuals cannot hear the very shrill

SEMICIRCULAR CANALS ; COCHLEA.— SENSE OF HEARING. 541

tones produced by particular Insects, or even Birds, which are dis-
tinctly audible to others.

952. Not only do we find the tympanic apparatus superadded, in
the higher forms of the organ of Hearing, but also the Semicircular
Canals, and the Cochlea. — The former exist in all Vertebrata, save
the lowest Fishes ; and in nearly every case, they are three in num-
ber, and lie in three different planes. Hence it has been supposed,
with some probability, that they assist in producing the idea of the
direction of sounds. The Cochlea does not exist at all in Fishes ; and
in Reptiles its condition is quite rudimentary. In Birds, this cavity
is more completely formed, though the passage is nearly straight
instead of spiral ; of its real character, however, there can be no doubt,
from its being divided, like the Cochlea of Man, by a membranous
partition, on which the ramifications of the auditory nerve are spread
out. This appendage has been supposed to be the organ, that enables
us to judge oii\ie pitch of sounds; an idea which derives some con-
firmation from the correspondence between the development of the
cochlea in different animals, and the variety in the pitch (or length of
the scale) of the sounds, which it is important that they should hear
distinctly, especially the voices of their own kind. — That the Vesti-
bule, with the passages proceeding from it, constitutes the true organ
of hearing, even in Man, is evident from the fact, that when (as not
unfrequently happens) the tympanic apparatus has been entirely de-
stroyed by disease, so as to reduce the organ to the condition of that
in which no such apparatus exists, the faculty of Hearing is by no
means abolished, though it is deadened.

953. The faculty of Hearing, like other senses, may be very much
increased in acuteness by cultivation ; but this improvement depends
rather upon the habit of attention to the faintest impressions made
upon the organ, than upon any change in the organ itself. This habit
may be cultivated in regard to sounds of some one particular class;
all others being heard as by an ordinary person. Thus, the watchful
North American Indian recognizes footsteps, and can even distinguish
between the tread of friends and foes ; whilst his white companion,
who has lived among the busy hum of cities, is unconscious of the
slightest sound. Yet the latter may be a musician, capable of dis-
tinguishing the tones of all the different instruments in a large orches-
tra, of following any one of them through the part which it performs,
and of detecting the least discord in the blended effects of the whole,
— effects which would be to the unsophisticated Indian but an indis-
tinct mass of sound. In the same manner, a person who has lived
much in the country, is able to distinguish the note of every species
of bird that lends its voice to the general chorus of nature; whilst the
inhabitant of a town hears only a confused assemblage of shrill sounds,
which may impart to him a disagreeable rather than a pleasurable
sensation.

954. In all continued sounds or tones^ there are several points to be
attended to. In the first place, we take cognizance of their pitch ;

542 OP THE SENSE OF SIGHT.

which depends upon the number of vibrations in a given time, — the
high notes being produced by the most rapid vibrations, and the low
notes by the slowest. The ear can appreciate tones produced by
24,000 impulses per second ; the pitch of which is about four octaves
above the highest F of the piano-forte. On the other hand, no
sequence of vibrations fewer than 7 or 8 in a second, can produce a
continuous tone ; because the impression left by each impulse has
passed away, before the next succeeds ; and there is consequently no-
thing more than a succession of distinct beats. — The strength or loud-
ness of musical tones depends (other things being equal) on the force
and extent of the vibrations, communicated by the sounding body to
the medium which propagates them. This will diminish, however,
with distance ; which softens loud tones by lowering the intensity of
the undulations, as a consequence of their more extensive diffusion.
The cause of the differences, in the timbre, or quality of musical tones,
— such, for instance, as those which exist between the tones of a flute,
a violin, a trumpet, and a human voice, all sounding a note of the
same pitch, — are unknown : but they probably depend upon differ-
ences of form in the undulations. — Our ideas of the direction and
distance of sounds, are for the most part formed by habit. Of the
former we probably judge in great degree, by the relative intensity of
the impressions received by the two ears ; though we may form some
notion of it by a single ear, if the idea just stated as to the use of the
semicircular canals (§ 952), be correct. Of the distance of the sound-
ing body, we judge by the intensity of the sound, comparing it with
that which we know the same body to produce when nearer to us.
The Ear may be deceived in this respect, as w^ell as the eye ; thus the
effect of a full band at a distance may be given by the subdued tones
of a concealed orchestra close by us ; and the Ventriloquist produces
his deception, by imitating as closely as possible, not the sounds
themselves, but the manner in which they would strike our ears.

6. Of the Sense of Sight.

955. By the faculty of Sight, we are made acquainted, in the first
place, with the existence of Light ; and by the medium of that agent,
we take cognizance of the form, size, colour, position, &c., of bodies
that transmit or reflect it. As to the mode in which luminous im-
pressions are propagated through space, philosophers are at present
undetermined ; and the question is of no physiological importance,
since all are agreed as to the laws which regulate their transmission.
These laws, which will be found at large in any Treatise on Natural
Philosophy,* may be briefly stated as follows.

I. Light travels in straight lines, so long as the medium through
which it passes is of uniform density.

II. When the rays of light pass from a rarer medium into a denser

• See Dr. Golding Bird's Manual, Chap. XXII.

LAWS OF TRANSMISSION OF LIGHT. 543

one, they are refracted towards a line drawn perpendicularly to the
surface they are entering.

III. When the rays of light pass from a denser medium into a rarer
one, they are refractedyrom the perpendicular.

IV. When rays proceeding from the several points of a luminous
object, at a distance, fall upon a double convex lens, they are brought
to a focus upon the other

side of it; in such a man- Fig.iso.

ner that an inverted pic-

ture of the object is formed c 3^==::^ ^^-^^^^^

upon a screen, placed in the "^^S^^^^^iXS^?'''^^"^-^^--^

proper position to receive it. ^ <^^<^^'jCr^'C ^^^^

Thus in Fig. 150, A B is \^^^^4^^^^^<>Z

the object, and E F the ^ ^^ ^-— ^^I::^

lens ; the rays issuing from
the two extremities and the

centre of the object, are brought to a corresponding focus at a less
distance on the other side of it, so as to form a distinct picture ; but
as the rays from a are brought to a focus at d, and those from b at c,
the picture will be inverted.

v. The further the object is removed from the lens, the nearer will
the picture be brought to it, and the smaller will it be.

VI. If the screen be not held precisely in the focus of the lens, but
a little nearer, or further off, the picture will be indistinct ; for the
rays which form it will either not have met, or they will have crossed
each other.

956. The Eye, in its most perfect form — such as it possesses in
Man and the higher animals, — is an optical instrument of wonderful
completeness; designed to form an exact picture of surrounding
objects, upon the Retina or expanded surface of the Optic nerve, by
which the impression is conveyed to the brain. The rays of light,
which diverge from the several points of any object, and fall upon the
front of the cornea, are refracted by its convex surface, whilst passing
through it into the eye, and are made to converge slightly. They are
brought more closely together by the crystaline lens, which they
reach after passing through the pupil ; and its refracting influence,
together with that produced by the vitreous humour, is such as to
cause the rays, that issued from each point, to meet in a focus on the
retina. In this manner, a complete inverted image is formed, as
shown in Fig. 151 ; which represents a vertical section of the eye,
and the general course of the rays in its interior. As in the preceding
figure, the rays which issue from the point a are brought to a focus
at D ; whilst those diverging from b are made to converge upon the
retina at c. The Retina, which is itself so thin as to be nearly trans-
parent, is spread over the layer of black pigment, which lines the
choroid coat. The purpose of this is evidently to absorb the rays of
light that form the picture, immediately after they have passed through
the retina ; in this manner, they are prevented from being reflected

544 OF THE EYE AS AN OPTICAL INSTRUMENT.

from one part of the interior of the globe to another ; which would
cause great confusion and indistinctness in the picture. Hence it is

that, in those albino individuals
'P'^g'^^^' (both of the Human race, and

among the lower animals), in
whose eyes this pigment is de-
ficient, vision is extremely im-
perfect, except in a very feeble
light ; for the vascularity of the
choroid and iris is such, as to give
to these membranes a bright red
hue, which enables them powerfully to reflect the light that reaches
the interior of the eye, when they are not prevented from doing so by
the interposition of the pigmentary layer.

957. The Eye is so constructed as to avoid certain errors and
defects, to which all ordinary optical instruments are liable. One of
these imperfections, termed spherical aberration, results from the fact,
that the rays of light, passing through a convex lens whose curvature
is circular, are not all brought to their proper foci; those which have
passed through the exterior of the lens being made to converge sooner
than those which have traversed its central portion. The result of
this imperfection is, that the image is deficient in clearness, unless
only the central part of the lens be employed. — The other source of
imperfection is what is termed chromatic aberration; and it results
from the unequal degree in which the differently coloured rays are
refracted, so that they are brought to a focus at different points. The
violet rays, being the most refrangible, are soonest brought to a focus;
and the red being the least refrangible, have their focus at the greatest
distance from the lens. Hence it is impossible to obtain an image by
an ordinary lens, in which the colours of the object are accurately
represented ; for the foci of its differently coloured portions will be
different ; and its white rays will be decomposed, so that the outlines
will be surrounded by coloured fringes. — The Optican is enabled to
correct the effects of these aberrations, by combining lenses of diflfer-
ent densities and curvatures ; so arranged as to correct each others'
errors, without neutralizing the refractive power. This is precisely
the plan adopted in the construction of the Eye ; which, when per-
fectly formed, and in a healthy state, forms an accurate picture of
the object upon the retina, free from either spherical or chromatic
aberration. This is effected by the combination of humors of differ-
ent densities, having curvatures precisely adapted to the required
purpose.

958. There are certain variations, however, in the conformation of
the Eye, which diminish the perfection of its rfesult. Thus the Cornea
may be too convex, and the whole retractive power too great; so that
the image of an object at a moderate distance is formed in front of
the retina, instead of upon it. When this is the case, a distinct image
can only be formed, by bringing the object nearer to the eye ; the

OP THE EYE AS AN OPTICAL INSTRUMENT. 545

effect of which will be, to throw^ the picture further back. Such an
eye is said to be myopic, or short-sighted ; and its imperfection may-
be corrected by placing a concave lens in front of the cornea, of a
curvature adapted to neutralize what is superfluous in the convexity
of the latter. — On the other hand, if the cornea be too flat, and the
refractive power of the humors be too low, the convergent rays pro-
ceeding from an object at a moderate distance will not meet upon the
retina, but behind it (if they were allowed to pass on); consequently,
the picture is indistinct ; and it can only be made clear, either by
withdrawing the object to a greater distance, which will bring the
focus of the eye nearer to its front, or by interposing a convex lens
to increase the refractive power of the eye. Such a condition is
termed presbyopic (from its being common in aged persons), or long-
sighted. It may proceed to such an extent, that not even the removal
of the object to any distance can permit the formation of a distinct
picture ; so that the assistance of a convex lens must be obtained,
even to see remote objects clearly; though a less degree of convexity
will be required than for the clear vision of nearer objects. This state
is particularly well-marked after the operation for cataract ; for the
removal of the crystaline lens so greatly diminishes the refractive
power of the eye, as to render necessary the assistance of convex
lenses of high curvature.

959. The power, by which a healthy well-formed eye can accom-
modate itself to the distinct vision of objects at varying distances, is
a very remarkable one ; and its rationale is not yet properly under-
stood. According to the laws already stated (§ 955, V. and VI.),
the picture of a near object can only be distinct when formed more
remotely from the lens than the picture of a distant object. Conse-
quently when the eye, that has been looking at a distant object, and
has seen it clearly, is turned to a near object, a distant picture of the
latter cannot be formed without some alteration, either in the distance
between the cornea and the retina, or in the curvature of its refractive
surfaces. Of the mode in which this adjustment is made, however,
nothing is certainly known ; the minuteness of the requisite amount
of alteration being such as to prevent its precise seat from being de-
termined.

960. The various humors and containing membranes of the Eye,
thus answer the purpose of a most delicate and self-adjusting Optical
instrument ; the sole part, which is immediately concerned in the act
of sensation, being the Retina, or net-like expansion of the Optic
nerve, which lies between the black pigment and the vitreous humor.
It is in this structure that the presence of cells at the peripheral as
well as the central extremities of the afferent nerves (§ 381), may be
most clearly demonstrated. They can scarcely be distinguished, in
many animals, from the cells of the vesicular matter of the brain ; and,
like the latter, they lie in the midst of a plexus of capillary blood-
vessels, which supplies the materials requisite for their growth and
activity. For the maintenance of the due nutrition of this organ, it is

35

646 VISUAL PERCEPTIONS.

requisite that it should be occasionally called into use. If its func-
tional power be destroyed, by opacity of
^'s- 152. the anterior portion of the eye, the nutri-

tion of the retina and optic nerve suffers
to such a degree that these parts cease
after a time to exhibit their characteristic
structure ; — thus showing that the general
rules already stated (Chap. VII.) in re-
gard to the connection between the func-
tional activity, and the due nutrition of
tissues and organs, hold good with re->
spect to the Nervous structure. — The
mode in which the vesicular layer of the
retina comes into relation with the net-
work of nerve-fibres, of which it chiefly

Distribution of Capillaries invascu- • *. i, t i. u i i

lar layer of Retina. consists, has not yet bccn clearly ascer-

tained.

961. The picture of external objects, which is formed upon the
Retina, closely resembles that which we see in a Camera Obscura. It
represents the outlines, colours, lights and shades, and relative posi-
tions, of the objects before us ; but these do not necessarily convey to
the mind the knowledge of their real forms, characters, or distances.
The perception of the latter, as already remarked (§ 936), is a mental
process ; and it may be intuitive, or acquired, — the latter, it w^ould
seem, being the general condition of the function in Man, the former
in the lower animals. The Infant is educating his perceptive powers,
long before any indications present themselves of the exercise of
higher mental faculties. By the combination, especially of the sen-
sations of sight and touch, he is learning to judge of the surfaces of
objects as they feel, by the appearance they present, — to form an idea
of their distance, by the mode in which his eyes are directed towards
them, — and to estimate their size, by combining the notions obtained
through the picture on the retina, with those he acquires by the move-
ment of his hands over their different parts. — A simple illustration
will show how closely the ideas excited by the two sets of sensations,
are blended in our minds. The idea of smoothness is one w^hich has
reference to the touch ; and yet it constantly occurs to us, on looking
at a surface which reflects light in a particular manner. On the other
hand, the idea of polish is essentially visual, having reference to the
reflection of light from the surface of the object; and yet it would
occur to us from the sensation conveyed through the touch, even in
the dark.

962. That this sort of combination is not intuitive in Man, but is
the result of experience, is evident from the numerous observations
made upon those, who had acquired the sense of Sight for the first
time, after long familiarity with the characters of objects as perceived
through the Touch. Thus a boy of four years old, upon w^hom the
operation for congenital cataract had been very successfully performed,

ERECT AND SINGLE VISION. 547

continued to find his way about his father's house, rather hy feeling
with his hands, as he had been formerly accustomed to do, than by
his newly-acquired sense of Sight; being evidently perplexed, rather
than assisted, by the sensations which he derived through it. But
when learning a new locality, he employed his sight, and evidently
perceived the increase of facility which he derived from it. Among
the many interesting particulars recorded of the youth, on whom
Cheselden operated with equal success, it is mentioned that, although
perfectly familiar with a dog and a cat by feeling them, and quite
able to distinguish between them by his sight, he was long before he
associated his visual with his tactual sensations, so as to be able to
name either animal by sight alone. — The question was put by the
celebrated Locke, whether a person born blind, who was able by
his touch to distinguish a cube from a sphere, would, on suddenly
obtaining his sight, be able to recognize each by the latter sense ;
the reply was given in the negative; and the experience of the cases
just referred to, as well as of many others, fully justifies such an
answer.

963. Still there are, even in Man, certain intuitive perceptions,
which aflford great assistance in the formation of ideas regarding ex-
ternal objects, through the visual sense. And the first of these is the
power by which we recognize their erect position, notwithstanding
the inversion of the image upon the retina. This is certainly not a
matter of experience ; nor is it capable of explanation (as some have
thought) by a reference to the direction in which the rays fall upon
the retina. It is the mind which rectifies the inversion ; and, as
already remarked, it is just as difficult to understand, how the inverted
image on the retina should be taken cognizance of by the mind at all,
as it is to comprehend how it should be thus rectified. In fact, there
is no real connection whatever, between the inversion of the image
upon the retina, and that wrong perception of external objects, which
some have thought to be its necessary consequence. Any distortion
of the picture, giving a wrong view of the relative positions of the
objects represented, v^ould be attended with a different result. — The
same may be said of the cause of the singleness of the sensation per-
ceived by the mind, although an image is formed upon the retina of
each eye, — of those objects, at least, which lie in the field of vision
that is common to both. This blending of the pictures formed upon
the two retinae into a single perception, appears to be, in part at least,
the effect of habit. For when the images do not fall upon the parts of
the two retinae, which are accustomed to act together, double vision is
the result. Thus if, when looking steadily at an object, we press one-
of the eyeballs sideways with the finger, we see two representations
of the object ; and the same thing frequently occurs as a result of an
affection of the nerves or muscles of one or both eyes, (as inordinary
strabismus or squinting,) or from some change in the nervous centres,
as in various disorders of the Encephalon, and in intoxication. If this
condition should be permanent, however, we usually find that the in-

548 COMBINATION OF PICTURES IN TWO EYES.

dividual becomes accustomed to the double images, or rather ceases
to perceive that they are double ; probably because the mind becomes
habituated to receive the impressions from the two parts of the retina,
which now act together. And if, after the double vision has passed
away, the conformity of the tw^o eyes be restored (as by the operation
for the cure of squinting) there is double vision for some little time,
although the two parts of the retina, which originally acted together,
are now brought into their pristine position.

964. But the images thus combined are far from being identical;
and one of the most remarkable of all our intuitive perceptions is that
by wdiich they are reconciled and combined, and are caused to give
rise to an idea, that differs essentially from either image. No near
object can be seen by the two eyes in the same manner ; of this the
reader may easily convince himself, by holding up a thin book in such
a manner that its back shall be in a line with the nose, and at a mo-
derate distance from it; and by looking at the book first with one
eye, and then w^ith the other. He will find that he gains a different
view of the object with each eye, when used separately ; so that if he
were to represent it as he actually sees it under these circumstances
he would have two perspective delineations differing from one another,
because draw^n from different points. But on looking at the object
with the two eyes conjointly, there is no confusion between these pic-
tures; nor does the mind dwell upon either of them singly; but the
union of the two intuitively gives us the idea of a solid projecting
body, — such an idea as we could only have otherwise acquired by the
exercise of the sense of touch. That this is really the case, has been
proved by experiments with a very ingenious instrument, the Stereo-
scope, invented by Prof. Wheatstone ; which is so contrived as to
bring to the two eyes, by reflection from mirrors, two different pic-
tures, such as would be accurate representations of a solid object, as
seen by the two eyes respectively. When the arrangement is such,
as to bring the images of these pictures to those parts of the retinae
which would have been occupied by the images of the solid (supposing
that to have been before the eyes), the mind will perceive, not one or
other of the single representations of the object, nor a confused union
of the tW'O, but a body projecting in reliefs the exact counterpart of
that from which the drawings were made. — Thus the combination of
the two pictures and the perception of an object different from either
of them, is effected by a mental process of an instinctive kind ; of the
nature of which we know nothing further.

965. When two pictures, representing dissimilar objects, are pro-
jected upon the retinae of the tw^o eyes by means of the Stereoscope,
the result is a curious one. The mind perceives only one of them,
the other being completely excluded for a time; but it commonly
happens that, after one has been seen for a short period, the other
begins to attract attention and takes its place, the first entirely dis-
appearing; so that there is no confusion or intermingling of images,
except at the moment of change. The Will may determine, to a

ESTIMATION OF DISTANCE OF OBJECTS. 549

certain extent, which object shall be seen ; but not entirely ; for if
one picture be more illuminated than the other, it will be seen during
a larger proportion of the time. — An interesting variation of this ex-
periment may be made, without the aid of the Stereoscope, by holding
a piece of blue glass before one eye, and a piece of yellow glass
before the other. The result will be, not that everything will be seen
of a green colour, but that the surrounding objects will be seen alter-
nately blue and yellow; — or sometimes the field of vision will be
blue, spotted with yellow ; alternating with yellow spotted with blue.
Thus, when we have two dissimilar objects before the eyes, our at-
tention cannot be kept upon either, to the exclusion of the other, but
is alternately and involuntarily directed, either in part or completely,
to one and the other.

966. Our idea of the distance of near objects is evidently acquired
from experience; and is suggested by the muscular sensations, which
are produced by the contraction of the adductor muscles of the eyes.
When we direct our eyes towards a near object, a certain degree of
convergence takes place between their axes; the degree increasing as
the distance between the object and the eyes diminishes; and vice
versa. We instinctively interpret the sensations thus produced, in
such a manner as to be able to compare, with great accuracy, the rela-
tive distances of two objects, that are not remote from the eyes. This
intuition, however, is evidently one of the acquired kind; as may be
seen by watching the actions of an infant, or of a person who has
recently become possessed of Vision. When an object is held before
the eyes and an attempt is made to grasp it, the manner in which the
attempt is made clearly shows, that there is no power of forming a
precise idea of its situation, such as that which exists in many of the
lower animals from their first entrance into the world (§ 938). The
impressions made upon the eyes have to be corrected by those received
through the touch, before the power of judging of distance is accom-
plished. How much this power depends upon the conjoint use of
both eyes, is evident from the difiSculty with which any actions, that
require an exact appreciation of distance, are performed by those who
have lost the sight of one eye, until they have acquired new modes of
judging of it.

967. In regard to remote objects, we have not the same guide ;
since the convergence of the eyes, in viewing them, is so slight that
the axes are virtually parallel. Our judgment of their distance is
chiefly founded upon their apparent size, if their actual size be known
to us ; and also upon the extent of ground, which we see to intervene
between ourselves and the object. But if we do not know their
actual size, and are so situated that we cannot estimate the interven-
ing space, we form our judgment chiefly from the greater or less dis-
tinctness of their colour and outline. Hence our idea of it will be
very much affected by varying states of the atmosphere ; a slight
haziness increasing the apparent distance ; whilst a peculiarly clear
state of the air will seem to cause remote objects to approach much

550 CHANGES IN SIZE OF PUPIL.

more closely. This want of convergence between the axes of the
two eyes, has the further effect of causing the pictures upon the two
retinae to be nearly identical ; and consequently the idea of projection
is not so strongly excited; nor are we able to distinguish with the
same certainty between a well-painted picture, in which the lights
and shades are preserved, and the objects themselves in relief.

968. Our notion of the size of an object is closely connected with
that of its distance. It is founded upon the dimensions of the picture
projected on the retina; and the dimensions of this picture will vary,
according to the laws of optics, (§ 955,) inversely as the distance, —
being, for example, twice as great when the object is viewed at the
distance of one foot, as when it is carried to the distance of two feet.
Where we know the relative distances of two objects, the estimation
of their real comparative sizes from their apparent sizes, is easily
effected by a simple process of mind; but this is not the case, when
we only guess at their distances : and our estimate of the size of
objects, even moderately remote, is as much affected by states of the
atmosphere as that of their distance, — the one being, in fact, propor-
tional to the other. Thus a slight mist, which gives the idea of in-
creased distance, will also augment the apparent size ; because, in
order that an object two miles off should produce a picture upon the
retina of the same extent with that made by an object one mile off,
it must have double the dimensions. It is evident that our perception
of the sizes of objects must be acquired by experience, in the same
manner as that of their distance has been shown to be.

969. We have now to consider briefly some other phenomena of
Vision, in which the acts of Mind, that have been just alluded to, do
not participate. — The contraction of the Pupil, under the stimulus of
light, seems to be affected by a sphincter muscle, which surrounds
the orifice, and which is put in action by a branch of the third pair of
nerves. This is an action with which the will has nothing to do ; and
it takes place entirely without our consciousness. Although it is due
to the stimulus of light, yet there is reason to believe that the con-
sciousness of the presence of light is not requisite ; and that it is,
therefore, a purely reflex action. The optic nerve seems to be the
channel through which the impression is conveyed to the nervous
centres ; and the third pair is that through which the motor impulse
is conveyed to the iris. But there is some ground for the idea, that
the fifth pair may in some degree convey the requisite stimulus, when
the optic nerve has been divided. How far the dilatation of the
pupil is a muscular action, or merely one which results from the elas-
ticity of the tissue of the iris, when the sphincter is relaxed, has not
been clearly ascertained ; the latter is probably the case, a perma-
nently dilated state of the pupil being usually seen in cases where,
from any cause, it is not affected by the stimulus of light. The con-
traction of the pupil is evidently destined to exclude from the interior
of the eye, such an amount of light as would be injurious to it ; whilst
its dilatation in opposite circumstances admits the greatest possi--

PERCEPTION OF COLOURS. 551

ble number of rays. There is a contraction of the pupils, however,
which takes place without any change in the amount of light. This
occurs when the two eyes are made to converge strongly upon any
object brought very near them ; and its purpose appears to be, to
prevent the rays from entering the eye at such a wide angle as would
render it impossible for them to be all brought to their proper foci,
and would thus produce an indistinct image.

970. In the use of the Eye, like that of the Ear, there is a ten-
dency to blend into one continuous image a succession of luminous
impressions made at short intervals ; upon which fact depend a num-
ber of cuVious optical illusions. The length of the greatest interval
that can elapse without an interruption of the presence of the image,
(in other words the duration of the visual impression,) may be mea-
sured by causing aluminous object to whirl round, and by ascertain-
ing the longest period that may be allowed for each revolution,
consistently with the completeness of the circle of light thus formed.
By experiments of this kind, the time has been found to vary, in dif-
ferent individuals, or in different states of the same individual, from
about l-4th to 1-lOth of a second : that is, the impression must be
repeated from four to ten times in each second, to insure the continu-
ousness of the image.

971. The impressions of variety of colour^ are produced by the
differently coloured rays, which objects reflect or transmit to the eye.
It is curious that some persons, whose sight is perfectly good for forms,
distances, &c., are unable to discriminate colours. This curious affec-
tion has received the name of Daltonism, from the circumstance that
the celebrated Dalton was an example of it. There are numerous
modifications of it; the want of power to discriminate colour being total
in some, whilst in others it extends only to certain shades of colour,
or to the complementary colours.

972. When the retina has been exposed for some time to a strong
impression of some particular kind, it seems less susceptible of feebler
impressions of the same kind; thus if we look at any brightly luminous
object, and then turn our eyes upon a sheet of paper, we shall per-
ceive a dark spot upon it, — the portion of the retina, which had receiv-
ed the brighter image, not being affected by the fainter one. — Again,
when the eyes have received a strong impression from a coloured
object, the spot which is seen when the eyes are directed upon a
white surface exhibits the complementary colour ; for the retina has
been so strongly affected in the part that originally received the image,
by its vivid hue, that it does not perceive the fainter hue of the
same kind in the object to which it is then turned, and it is impressed
only by the remaining rays forming the complementary colours.
This explanation applies to the phenomena of the coloured shadows
which are often seen at sunset, and of those which may be seen in a
room whose light enters through coloured glass or drapery. For if the
prevailing light be of one colour, — orange or red for instance, — the
eye will not take cognizance of that colour in the faint light of the

552 OF THE VOICE AND SPEECH.

shadows ; and will see only its complement, blue or green. If the
shadow be viewed through a tube, in such a manner that the general
coloured ground is excluded, it presents the ordinary tint.

CHAPTER XIV.

OF THE VOICE, AND SPEECH.

973. There is one particular application of Muscular power in Man,
which deserves special consideration, as being that by which he effects
his most complete and intimate communication with his fellows ; —
that, namely, by which his organ of Voice is put into action. In all
air-breathing Vertebrata, the production of sound depends upon the
passage of air through a certain portion of the respiratory tubes; which
is so constructed as to set it in vibration, as it passes forth from the
lungs. — In Reptiles, the vibrating apparatus is situated at the point,
where the trachea opens into the front of the pharynx ; it is of very
simple construction, however, being only composed of a slit bounded
by two contractile lips; and few of the animals of this class can pro-
duce any other sound than a hiss, which, owing to the great capacity
of their lungs, is often very much prolonged. — In Birds, the situation
of the vocal organ is very different. The trachea opens into the front
of the pharynx, as in Reptiles, by a mere slit ; the borders of which
have no other movement than that of approaching one another, so as
to close the aperture when necessary. This appears to be the instru-
ment for regulating the ingress and egress of air, in conformity with
the wants of the respiratory function. The vocal larynx of Birds is
situated at the lower extremity of the trachea, just where it subdivides
into the bronchial tubes; and it is of very complex construction, espe-
cially in the singing birds. In Mammalia, on the other hand, the
vocal organ and the regulator of the respiration are united in the
larynx, which is situated at the top of the trachea. There are few, if
any, of this class, which have not some vocal sound ; but the variety
and expressiveness which can be given to it, differ considerably in the
several orders ; being by far the greatest in Man, who alone, there is
reason to believe, has the power of producing articulate sounds, or
proper language.

974. The Larynx is built up, as it were, upon the Cricoid cartilage
(Fig. 153, X w r u), which surmounts the trachea, and which might
be considered as its highest ring, modified in form, its depth from
above downwards being much greater posteriorly than anteriorly.
This is embraced, as it were, by the Thyroid cartilage (g e h); which
is articulated to the sides of the Cricoid by its lower horns, round the
extremities of which it may be considered to rotate, as on a pivot. In

STRUCTURE OF THE LARYNX.

553

this manner, the front of the Thyroid cartilage may be lifted up, or de-
pressed, by the muscles which act upon it; whilst the position of its
posterior part is but little

changed. Upon the upper Fig. 153.

surface of the back of the ep

Cricoid cartilage, are seated i

the two small Arytenoid car-
tilages (n f) ; these are so
tied to the cricoid by a bun-
dle of strong ligaments (b
b), as to have a sort of rota-
tion upon an articulating
surface, which enables them
to be approximated or sepa-
rated from each other, —
their inner edges being
nearly parallel in the first
case, but slanting away from
each other in the second.
To the summit of these car-
tilages are attached the
ChordcB vocales, or vocal
ligaments (t u) composed of
yellow fibrous or elastic tis-
sue. These stretch across
to the front of the Thyroid
cartilage; and it is upon their
condition and relative situation, that the absence or the production of
vocal tones, and all their modifications of pitch, depend. They are
rendered tense by the depression of the front of the Thyroid carti-
lage, and relaxed by its elevation ; by which action the pitch of the
tones is regulated. But for the production of any vocal tones what-
ever, they must be brought into a nearly parallel condition, by the
mutual approximation of the points of the arytenoid cartilages to
which they are attached ; whilst in the intervals of vocalization, these
are separated, and the rima glottidis, or fissure between the chordae
vocales, assumes the form of a narrow V, with its point directed
backwards.

975. Thus there are two sets of movements concerned in the act of
vocalization : — the regulation of the relative position of the Vocal
Cords, which is effected by the movements of the Arytenoid carti-
lages;— and the regulation of their tension, which is determined by
the movements of the Thyroid cartilage. The Arytenoid cartilages are
made to diverge from one another by means of the Crico-arytenoidei
postici of the two sides, (n /, n /,) which proceed from their outer cor-
ners and turn somewhat round the edge of the Cricoid, to be attached
to the lower part of its back ; their action is to draw the outer corners
of the Arytenoid cartilages outwards and downwards, so that the

Bird's-eye view of larynx from above, after Willis:
— G E H, the thyroid cartilage, embracing the ring of
the cricoid rw x w, and turning upon the axis xz,
which passes through the lower horns ; n f, n f, the
arytenoid cartilages, connected by the arytenoideus
transversus ; T v, T v, the vocal ligaments ; N x, the
right crico- arytenoideus lateralis (the left being re-
moved) ; V kf, the left thyro-arytenoideus (the right
being removed) ; N Z, N Z, the crico-arytenoidei pos-
tici ; B B, the crico-arytenoid ligaments.

554 REGULATION OF THE APERTURE OF THE GLOTTIS.

points to which the vocal ligaments are attached are separated from
one another, and the rima glottidis is thrown open. The action of
these muscles is antagonized by that of the Arytenoideus transversus^
which draws together the Arytenoid cartilages ; and by that of the
Crico-arytenoidei laterales of the two sides, (n x,) which run forwards
and downwards from the outer corners of the Arytenoid cartilages,
and tend by their contraction to bring together their anterior points,
to which the Vocal ligaments are attached. — The depression of the
front of the Thyroid cartilage, and the consequent tension of the Vocal
ligaments, is occasioned by the conjoint action of the Crico-thyroidei
of the two sides, which occasions the Thyroid and Cricoid cartilages
to rotate, the one upon the other, at the articulation formed by the
inferior cornua of the former ; and this action will be assisted by the
SternO'thyroideiy which tend to depress the front of the Thyroid car-
tilage, by pulling from a fixed point below. On the other hand, the
elevation of the front of the Thyroid cartilage, and the relaxation of
the Vocal ligaments, are effected by the contraction of the Thyro-
arytenoidei of the two sides (v kf), whose attachments are the same
as those of the Vocal ligaments themselves ; and this is aided by the
Thyro-hyoidei, which will tend to draw up the front of the Thyroid
cartilage, acting from a fixed point above.

976. The muscles which govern the aperture of the glottis, — those
namely, which separate and bring together the arytenoid cartilages,
and thus widen or contract the space between the posterior extremi-
ties of the vocal ligaments, — have important functions in connection
with the Respiratory actions in general, and stand as guards, so to
speak, at the entrance to the lungs. We can entirely close the
glottis, through their means, by an effort of the Will, either during
inspiration or expiration ; and it is a spasmodic movement of this sort,
which is concerned in the acts of Coughing and Sneezing, the purpose
of which is to expel, by a sudden and powerful blast of air, any irri-
tating substances, whether solid, liquid, or gaseous, which have found
their way into the air-passages. These muscles appear to be under
the sole direction of the inferior or recurrent laryngeal nerve ; which
seems to possess exclusively motor endowments. When this nerve
is divided, on each side, or when the par vagum is divided above its
origin, the muscles of the larynx (with the exception of the crico-
thyroid) are paralyzed ; and the aperture of the glottis may remain
open, or may be entirely closed, according to the manner in which its
lips are aff*ected by the currents of air in egress or ingress. It is
found that, under such circumstances, tranquil respiration may be
carried on ; but that any violent ingress or egress of air will tend to
drive the lips of the glottis (these being in a state of complete relaxa-
tion) into apposition with each other, so as completely to close the
aperture. The character of the superior laryngeal nerve appears to
be almost exclusively afferent ; no muscle, except the crico-thyroid,
being thrown into contraction when it is irritated ; whilst, on the
other hand, if it be divided, neither the act of coughing, nor any

PRODUCTION OF VOCAL SOUNDS. 555

reflex respiratory movement whatever, can be excited, by irritating
the lining membrane of the larynx.

977. Daring the ordinary acts of inspiration and expiration, the
Chordae vocales appear to be widely separated from each other, and
to be in a state of the freest possible relaxation. In order to produce
a vocal sound, they must be made to approach one another, and their
inner faces must be brought into parallelism ; both of which ends are
accomplished by the rotation of the Arytenoid cartilages ; whilst, at
the same time, they must be put into a certain degree of tension, by
the depression of the Thyroid cartilage. Both of these movements
take place consentaneously, and are mutually adapted to each other ;
the vocal ligaments being approximated, and the rima glottidis con-
sequently narrowed, at the same time that their tension is increased.
There is a certain aperture, which is favourable to the production of
each tone, although the pitch itself is governed by the tension of the
Vocal Cords ; and it is, perhaps, to a want of consent between the
two, that the peculiarly discordant nature of some voices, which appear
incapable of producing a distinct musical tone, is due.

978. It has been fully proved, by the researches of Willis, Miiller,
and others, that the action of the Vocal ligaments, in the production of
sound, bears no resemblance to that of vibrating strings ; and that it
is not comparable to that of the mouth-piece of the flute-pipes of the
Organ : but that it is, in all essential particulars, the same with that
of the reeds of the Hautboy or Clarionet, or the tongues of the Accor-
dion or Concertina. All the phenomena attending the production of
Musical tones are fully explicable on this hypothesis; except the pro-
duction oi falsetto notes, which has not yet been clearly accounted
for. — The power which the Will possesses, of determining, with the
most perfect precision, the exact degree of tension w-hich these liga-
ments shall receive, is extremely remarkable. Their average length
in the Male, in the state of repose, is estimated by Miiller at about
73-lOOths of an inch; whilst, in the state of greatest tension, it is
about 93-lOOths; the whole difference, therefore, is not above 20-
lOOths, or one-fifth of an inch. In the female glottis, their average
dimensions are about 51-lOOths and 63-lOOths, respectively ; so that
the difference is here only 12-lOOths, or less than one-eighth of an
inch. Now the natural compass of the voice, in most persons who
have cultivated the vocal organ, may be stated at about two octaves,
or 24 semitones. Within each semitone, a singer of ordinary capa-
bility could produce at least ten distinct intervals ; so that for the total
number of intervals, 240 is a very moderate estimate. There must,
therefore, be at least 240 diflferent states of tension of the vocal cords,
every one of which can be at once determined by the will, when a dis-
tinct conception exists of the tone to be produced (§ 904); and, as the
whole variation in their length is not more than one-fifth of an inch,
even in Man, the variation required, to pass from one interval to an-
other, will not be more than l-1200lh of an inch. — And yet this esti-
mate is much below that, which might be truly made from the per-

556 REGULATION OF THE PITCH OF VOCAL SOUNDS.

formance of a practiced vocalist. The celebrated Madame Mara is
said to have been able to sound 50 different intervals between each
semitone ; the compass of her voice was at least 40 semitones, so that
the total number of intervals w^as 2000. The extreme variation in
the length of the vocal cords, even taking the larger scale of the Male
larynx, not being more than the fifth of an inch, it may be said that
she w^as able to determine the contractions of her vocal muscles to
the ten-thousandth of an inch.

979. It is on account of the greater length of the Vocal cords, that
the pitch of the voice is much lower in Man than in Woman : but this
difference does not arise until the end of the period of childhood, —
the size of the larynx being about the same in the Boy and Girl, up to
the age of 14 or 15 years, but then undergoing a rapid increase in
the former, whilst it remains nearly stationary in the latter. Hence it
is that Boys, as well as Girls and Women, sing treble; whilst Men
sing tenor J which is about an octave lower than the treble ; or hass^
which is several notes lower still. — The cause of the variations in the
timbre or quality in different voices, is not certainly known ; but it
appears to be due, in part, to differences in the degree of flexibility
and smoothness in the cartilages of the larynx. In women and
children, these cartilages are usually soft and flexible, and the voice
is clear and smooth ; whilst in men, and in women whose voices have
a masculine roughness, the cartilages are harder, and are sometimes
almost completely ossified. The loudness of the voice depends in
part upon the force with which the air is expelled from the lungs ;
but the variations in this respect, which exist among different indi-
viduals, seem partly due to the degree in which its resonance is
increased by the vibration of the other parts of the larynx, and of the
neighbouring cavities. In the Howling Monkeys of America, there
are several pouches opening from the larynx, which seem destined to
increase the volume of tone that issues from it; one of these is exca-
vated in the substance of the hyoid bone itself. Although these
Monkeys are of inconsiderable size, yet their voices are louder than
the roaring of lions, and are distinctly audible at the distance of two
miles; and when a number of them are congregated together, the
effect is terrific.

980. The vocal sounds produced by the action of the larynx are
of very different characters ; and may be distinguished into the cry,
the song, and the ordinary or acquired voice. The cry is generally a
sharp sound, having little modulation or accuracy of pitch, and being
usually disagreeable in its timbre or quality. It is that by which ani-
mals express their unpleasing emotions, especially pain or terror; and
the Human infant, like many of the lower animals, can utter no other
sound. — In song, by the regulation of the vocal cords, definite and
sustained musical tones are produced, which can be changed or mo-
dulated at the will of the individual. Different species of Birds have
their respective songs ; which are partly instinctive, and partly ac-
quired by education. In Man, the power of song is entirely acquired j

VARIOUS KINDS OF VOCAL SOUNDS. 557

but some individuals possess a much greater facility in acquiring it
than others, — this superiority appearing to depend upon their more
precise conception of the tones to be sounded, as well as their more
ready imitation, — besides differences in the construction of the larynx
itself. The larynx of an accomplished vocalist, obedient to the ex-
pression of the emotions, as well as to the dictates of the will, may
be said to be the most perfect musical instrument ever constructed. —
The voice is a sound more resembling the cry, in regard to the absence
of any sustained musical tone ; but it differs from the cry, both in the
quality of its tone, and in the modulation of which it is capable by
the will. In ordinary conversation, the voice passes through a great
variety of musical tones, in the course of a single sentence, or even
a single word, — sliding imperceptibly from one to another ; and it is
when we attempt to fix it definitely to a certain pitch, that we change
it from the spea/dng to the singing tone.

981. The power of producing articulate sounds, from the combina-
tion of which Speech results, is altogether independent of the Larynx ;
being due to the action of the muscles of the mouth, tongue, and pa-
late. Distinctly articulate sounds may be produced without any vocal
or laryngeal tone, as when we whisper ; and it has been experiment-
ally shown, that the only condition necessary for this mode of speech,
is the propulsion of a current of air through the mouth, from back to
front. On the other hand, we may have the most perfect laryngeal
tone without any articulation ; as in the production of musical sounds,
not connected with words. But in ordinary speech, the laryngeal
tone is modified by the various organs, which intervene between the
larynx and the os externum. The simplest of these modifications is
that by which the Vowel sounds are produced : these sounds being
continuous tones modified by the form of the aperture through w^hich
they pass out. Thus, let the reader open his mouth to the widest
dimensions, depress the tongue, and raise the velum palati, so as to
make the exit of air as free as possible ; on then making a vocal
sound, he will find that this has the character of the vowel a in ah.
On the other hand, if he draw together the lips, still keeping the
tongue depressed, he will pass to the sound represented in the Eng-
lish language by oo, in the Continental languages by u. By atten-
tion to the production of other vowel sounds, it will be found that
they are capable of being formed by similar modifications in the form
of the buccal cavity and the size of the buccal orifice; and that they
are capable of being sustained for any length of time. There is an
exception, however, in regard to the sound of the English i, as in
fine; which is, in reality, a diphthongal sound, produced in the act
of transition from a peculiar indefinite murmur to the sound of the
long e, which takes its place when w^e attempt to continue it. The
short vowel sounds, moreover, — such as a in Jat, e in met, o in pot,
&c., are not capable of being perfectly prolonged ; as they require,
for their true enunciation, to be immediately followed by a consonant.
— A tolerably good artificial imitation of Vowel sounds has been

558 VOWELS AND CONSONANTS.— STAMMERING.

effected, by means of a reed-pipe representing the larynx, surmounted
by an India-rubber ball, with an orifice, representing the cavity and
orifice of the mouth. By modifying the form of the ball, the different
vowels could be sounded during the action of the reed.

982. In the production of the sounds termed Consonants, the breath
suffers a more or less complete interruption, in its passage through
the parts anterior to the larynx. The most natural primary division
of these sounds is into those which require a total stoppage of the
breath at the moment previous to their being pronounced, and which,
therefore, cannot be prolonged ; and those in pronouncing which the
interruption is partial, and which can, like the vowel sounds, be pro-
longed ad libitum. The former have received the designation of
explosive consonants ; the latter are termed continuous. — In pronoun-
cing any consonants of the explosive class, the posterior nares are com-
pletely closed ; and the whole current of air is directed through the
mouth. This may be checked by the approximation of the lips, as
in pronouncing b andp; by the approximation of the point of the
tongue to the front of the palate, as in pronouncing d and t ; or by
the approximation of the middle of the tongue to the arch of the
palate, as in pronouncing the hard g or k. The difference between
6, d, and g, on the one hand, and p, t, and k, on the other, depends
simply upon the greater extent of the meeting surfaces in the former
case than in the latter. — In sounding some of the continuous conso-
nants, the air is not allowed to pass through the nose ; but the inter-
ruption in the mouth is incomplete ; this is the case with v andjT, s
and z. In others, the posterior nares are not closed, and the air has
a nearly free passage, either through the nose alone, as in m and w,
or through the nose and mouth conjointly as in / and r. The sound
of k is a mere aspiration, caused by an increased force of breath;
and that of the guttural ch, as it exists in Welsh, Gaelic, and most
Continental languages, is an aspiration modified by the elevation of
the tongue, which causes a slight obstruction to the air, and an in-
creased resonance in the back of the mouth.

983. The study of the mode in which the different Consonants are
produced, is of particular importance to those who labour under
defective speech, especially that difficulty which is known as Slam-
mering. This very annoying impediment is occasioned by a want
of proper control over the muscles concerned in Articulation ; which,
instead of obeying the Will, are sometimes affected with an involun-
tary or spasmodic action, that interrupts the pronunciation of particular
words, — ^just as, in Chorea, the muscles of the limbs are interrupted
by spasmodic twitchings, in the performance of any voluntary move-
ment. In fact, persons affected with general Chorea, frequently
stammer ; showing that ordinary Stammering may be considered as a
kind of local Chorea. The analogy between the two states is further
indicated by the corresponding influence of excited Emotions in
aggravating both. — It is in the pronunciation of the consonants of
the explosive class, that the stammerer usually experiences the greatest

STAMMERING. 559

difficulty; forthe total interruption to the breath, which they occasion,
is frequently continued involuntarily;* so that either the expiration is
entirely checked, the whole frame being frequently thrown into the
most distressing serai-convulsive movements, or the sound comes out
in jerks. Sometimes, however, the spasmodic action occurs in the
pronunciation of vowels and continuous consonants; the stammerer
prolonging his expiration, without being able to check it.

984. The best method of curing this defect (where there is no mal-
formation of the organs of speech, but merely a want of power to use
them aright), is to study the particular difficulty under which the
individual labours ; and then to cause him to practise systematically
the various movements concerned in the production of the sounds in
question, at first separately, and afterwards in combination, — until
he feels that his voluntary control over the muscles is complete. The
patient would at first do well to practise sentences, from which the
explosive consonants are omitted ; his chief difficulty, arising from
the spasmodic suspension of the expiratory movement, being thus
avoided. Having mastered these, he may pass on to others, in which
the difficult letters are sparingly introduced ; and may finally accustom
himself to the use of ordinary language. One of the chief points
to be aimed at, is to make the patient feel that he has command
over his muscles of articulation ; and this is best done, by gradually
leading him from that which he can do, to that which he fears to
attempt.

• The interruption of the expiratory movement in Stammering, is usually stated
to take place in the glo/tis ,- but the Author is satisfied that, in all ordinary cases at
least, it is in that condition of the mouth which is preparatory to the pronunciation
of one of the explosive consonants.

INDEX.

N. B. The Numbers refer to the Paragraphs.

Aberration, corrected in eye, 957.
Absorbent Cells, 241-244.

« Vessels, 489.
Absorption, from alimentary canal, 489, 490;
by lacteals, 241-244; by blood-
vessels, 491-493.
** from general and pulmonary

surfaces, 522, 523.
** interstitial, by lymphatics, 502,

503; by blood-vessels, 502,
503.
Acalepha, circulation in, 550.
Adipose tissue, 259-263, 423-425.
Air-cells of lungs, 676-679.
Albumen, 173-175.

" conversion of into fibrin, 519.
Albuminuria, 533, 728.
Aliment, sources of demand for, 406-415.
" effect of variations in supply of,

416-426.
<* relative value of different kinds of,

427, 441.
" necessity for mixture in, 437.
Allantois, formation of, 817.
Amnion, formation of, 816.
Amphioxus, see Lancelot.
Anterior Pyramids, 890.
Apoplexy, 688, 922.
Area pellucida, 808.
Areolar tissue, 194-196, 205.
Arteries, movement of Blood in, 582-588.
" elasticity of, 583; tonicity of, 584;
contractility of, 585; pulsation of,
583, 584.
" anastomosis of, 588.
Articulata, circulation in, 552, 553; respi-
ration in, 657-660; nervous system in, 657
-660.
Articulate speech, 981, 982.
Asphyxia, 628, 703-709.
Assimilating cells, 212, 514, 519.
Assimilation, 519.
Asthma, 678.
Atrophy, 619, 620.
Attention, effects of, 935.
Auditory ganglia, 900.
" nerve, 949.

36

Azotized Compounds in Plants, 169, 428, 429.
« " in Animals, 428, 429.

*' " destination of in food,

429, 431, 433.

B

Basement membrane, 206-209.

Batrachia, respiration of, 670, 671.

Bile, composition and properties of, 724-726.

" uses of, in digestion, 476-479.
Birds, circulation in, 564, 565; respiration

in, 672-674; lymphatic system in, 500;

nervous centres of, 872; heat of, 761.
Blood, composition of, 525-529; uses of seve-
ral constituents of, 529, 530; changes
of, in disease, 531-534.

" corpuscles of, white, 212; red, 215-
223.

" coagulation of, 535.

« buffy coat of, 536, 537.

** rate of movement of, 577.

** influence of respiration on, 609-702.
Blushing, 603.

Bone, structure and composition of, 277-289.
Brunner's glands, 450.
Buffy coat of blood, 536, 537.
Butyric acid, 430.

Cancelli of Bone, 281.
Cancer-cells, 248.

Capillaries, movement of Blood in, 589-604;
variations in its rate, 597.
" variations in size of, 595, 603;

influence of nerves upon, 603,
604.
** independent force generated in,

598-600.
Carbonic acid, necessity for excretion of, 641;
sources of, in Animal bo-
dies, 642-648.
" " mode of its extrication, 649-
652; amount set free, 691-
698.
Cartilage, 264-273.

562

INDEX.

Cartilage, ossification of, 300-303.
Casein, 176, 832.
Catamenia, 798, 799.

Cell^ Vegetable, general history of, 30-45.
*' Animal, general history of, 211-214.
" isolated, various forms of, 210-216.
** the immediate agents in Organic func-
tions, 245, 246.
" union of, 247-254.
" coalescence of, 255-257.
" changes of form in, 258.
Cellular cartilage, 267, 268.
Cementum, 319.

Centipede, experiments on, 858.
Cerebellum, 867, 869.

" functions of, 911-914.

Cerebric acid, 383.
Cerebrum, 867, 868.

« functions of, 915-925.

Chlorosis, state of blood in, 219, 533, 537.
Cholesterine, 724.
Chondrine, 264, 265.
Chorda dorsalis, 254, 812.
Chordaj vocales, 974-979.
Chorea, 983.
Chorion, 795, 809, 818.

Chyle f composition and properties of, 515-
519.
« corpuscles of, 212, 518, 519.
Chyme, 472, 476.
Cicatricula, 808.
Cilia, 234, 235.
Cineritious substance, 379.
Circulation, 538,539; iji Plants, 540-548;
in lowest Animals, 549, 550 ;
in Echinodermata, 552; in
Articulata, 552, 553; in Mol-
lusca, 555-557; in Fishes,
558-561; in Reptiles, 562,
563; in Birds and Mammals,
564, 565.
" in early embryo, 551 , 554, 566;

in foetus at birth, 823, 824.
Coagulation of Albumen, 173, 174.
" of Blood, 535.

" of Casein, 176.

« of Fibrin, 180-187.

Cochlea, 952.

Csecum, secondary digestion in, 4S1.
Cold, degree of, sustainable by Plants, 110,
111.
" degree of, sustainable by Animals, 136.
Colostrum, 835.
Colours, perception of, 971,
Commissures of brain, 917-919.
Complementary colours, 972.
Conchifera, nervous system of, 852, 853.
Concussion, 581.
Congestion, 601, 602.

'< venous, 609, 610. •

Consensual actions, 903-905.
Consonants, 982.
Contractility of Muscle, 347.

« Vegetable tissues, 345, 346.

Convulsive actions, 885.
Cornea, 274.
Corpora Malpighiana, 728.

<« Quadrigemina, 873, 900, 902.
*' Striata, 901.

Corpora Wolffiana, 727.
Corpuscles of Blood; red, 215-223; white,
212.
" of Chyle and Lymph, 212.

Cortical substance of brain, 380.
Cranium, circulation in, 611.
Crura cerebri, 901.
Crustacea, geographical distribution of, 130;

respiration of, 658.
Crusta petrosa, 319.
Crystaline lens, 275.
Cuttle-fish, nervous cords in arras of, 854.

Daltonism, 971.

Death, somatic, 65, 68, 69, 628, 629.
" molecular, QQ, 67.

Decidua, 810, 811.

Defecation, 462, 463.

Deglutition, 453, 454, 897.

Dentine, 311-316.

Determination of blood, 601.

Development of Embryo, 805 et seq.

Diffusion, mutual, of gases, 650.

Digestion, organs of, 442-450.

" nature of the process, 472.

Disintegration of tissues, 617.

*' of Muscular tissue, 361.

" of Nervous tissue, 384.

Distances, estimate of, 966, 967.

Doris, gills of, 651, 656.

Double vision, 963.

Draper, Prof., his views on the capillary cir-
culation, 545-548, 598, 599.

Dreaming, 923.

Duration of pregnancy, 825, 826.
" of impressions on Ear, 956.
" of impressions on Eye, 970.

Dytiscus, experiments on, 859.

Ear, structure of, 956-960.
Echinodermata, circulation in, 552.
Electricity, development of in Animals, 771-
777; in Torpedo and Gymno-
tus, 771-775; in Muscles, 775;
in Frog, 776; in higher ani-
mals, 777.
" influence of, on organic func-

tions, 142, 146; efi'ects of
shocks of, 145-147.
*< influence of, on Muscles, 351

on sensory nerves, 932.
Embryo, early development of, 805 — 808
formation of vertebral column in
812; formation of vessels in, 813
formation of heart in, 814; forma
tion of digestive cavity in, 815
circulation in, 551, 554, 556.
Emotional movements, 906-908.
Emotions, influence of on hunger, 483; on
salivary secretion, 467; on heart's action,
580; oncapillary circulation, 603; on mam-
mary secretion, 836, 837.
Enamel, 317, 318.

INDEX.

563

Endosmose, 491, 492.
Entozoa, circulation in, 549, 550.
Epidermis, 224-228.
Epilepsy, 886.
Epithelium, 231-239.
Erect vision, 963.

Exhalation of water, from lungs, 701; from
cutaneous surface, 743-746.
" of organic matter, 702.

Excreting processes, general review of, 757-

759.
Eye, structure of, 956-960.

Facial nerve, 888.
Fat, 259-263, 423-425.
Fecundation of Ovum, 803, 804.
Ferments, action of, on blood, 534.
Fertilization of ovum, 803, 804.
Fibre, white, 189, 190.

« yellow, 189, 192.
Fibrillation, 183, 213.
Fibrin, coagulation of, 180-187.

« composition of, 178, 179.

*^ production of, 519.
Fibrous membranes, 188.
Fibrous tissues, simple, 188-193.
Fibro-Cartilage, 188, 269, 272.
Fifth Pair, 686, 888.
Fishes, lymphatic system in, 499; circulation

in, 558-561; respiration in, 663-667; heat

of, 761; electricity of, 771-774; nervous

centres in, 869, 870.
Fostus, circulation in, 822-824.
Follicles of glands, 238, 714-719.
Follicles of Lieberkiihn, 449.
Food, see Aliment.

Gall-bladder, 481.

Ganglion, 380.

Gangrene, 633, 634.

Gases, mutual diffusion of, 650.

Gastric fluid, properties and actions of, 468-

472.
<« *« conditionsof its secretion, 474,

475.
Gastric follicles, 470.
Gelatin, 190, 191, 429.
Geographical distribution of Animals, 130.

*' distribution of Plants, 102-106.

Germinal membrane, 806.
Gestation, duration of, 825, 826.
Gills," structure of, 651, 655, 656, 663.
Glands, essential parts of, 238, 714-719.
Globuline, 221.

Glosso-pharyngeal nerve, 888, 897,
Glottis, regulation of aperture of, 976.
Glycerine, 261.
Gout, 422, 615.
Graafian Vesicle, 796.
Granulation, 636.
Gravity, influence of on venous circulation,

609, 610.
Gray matter of nerves, 379.
Gymnotus, 771, 774.

H

Haematine, 221, 222.
Hair, 328-330.
Haversian canals, 282.
Hearing, sense of, 949-954.
Heart, action of, 668-570; sounds of, 571-
575; propulsive power of, 576-578;
frequency of contractions of, 579.
** power of, independent of nervous
agency, 580 ; influenced by mental
emotions, 580; by state of nervous
system, 581.
" first development of, in embryo, 814.
Heat, amount developed in Insects, 123; in
Fishes, 760; in Birds, 761; in Mam-
mals, 761; in Plants, 762.
** development of, chiefly dependent on
production of carbonic acid, 764; but
partly on other oxidizing processes,
765; inferior in young animals, 766.
** of body, kept down by perspiration,

745, 768.
" its influence upon vital activity in gene-
ral, 97, 98; upon Vegetation, 99-111;
upon Animal life, 112-141.
" degree of, sustainable by Animals, 138
-141; by Plants, 108.
Hippuric acid, 734,
Hunger, sense of, 483, 485.
Hybernation, 120, 121.
Hydra, stomach of, 443.
Hydrophobia, 886, 908.
Hypertrophy, 617, 618.
Hypoglossal nerve, 888.
Hysteria, 741, 887, 908.

Incubation, heat supplied in, 125-127.

Inflammation, nature of the process, 631, 632;
state of the blood in, 531, 536.

Inorganic substances in food, 438-441.

Insalivation, 446, 451, 452,

Insects, circulation in, 552; respiration in,
659, 660; nervous system of, 856-864; re-
flex actions of, 859, 860; instinctive actions
of, 860, 861; heat of, 123,

Instinctive actions of Man, 906.

Intelligence, 916.

Intercellular substance, 247, 253.

Intestinal canal, structure of, 447-450; move-
ments of, 460, 461.

Iris, movements of, 969.

Irritability of Muscles, 348-363.

Kidneys, structure of, 727, 728 ; action of,
729-741.

Lacteal s, 481, 496, 499.
Lactic acid, 735.
Lacuna of Bone, 279.

564

INDEX.

Lancelot, 254,661,869.
Laryngeal nerves, 976.
Larynx, structure and actions of, 974, 979.
Lead-palsy, 614.

Light, laws of transmission and refraction of,
955.

«' influence of on Vegetation, 79-92; on
growth and development of animals,
93-96.

" emission of, by animals, 770; by man,
771.
Lime, in Animal body, 438, 440, 441.
Lithic acid diathesis, 422, 732, 733.
Liver, structure of, 720-723; actions of, 477-

479, 724-726.
Luminousness, animal, 770, 771.
Lungs, structure of, 676-679.
Lymph, composition and properties of, 515,

520.
Lymphatics, 498-503.

M

Male, action of in reproduction, 785-790.

Malignant diseases, 640.

Malpighian bodies, of Kidney, 728; of Spleen,

506.
Mammalia, lymphatic system in, 500; circu-
lation in, 564, 565; respiration in, 674, 675;
heat evolved in, 761; nervous centres of,
873; ovisac of, 795.
Mammary glands, 830, 831.
Margarine, 261.

Mastication, act of, 451, 452, 896.
Medulla Oblongata, structure of, 889-893;

functions of, 894-899.
Memory, 924.

Menstrual secretion, 798, 799.
Mesenteric glands, 496.
Metamorphosis of animals, 407, 791, 792.
Milk, 436; composition and properties of,
832-834.
" circumstances influencing secretion of,
836, 839.
Mineral ingredients of food, 438-441.
Moisture, proportion of, in different parts of
the body, 149-152; influence of, on growth
of Plants and Animals, 153-157; effects of
withdrawal of, 158-161.
MoLLUSCA, circulating system of, 555-557;
respiratory organs of, 654-656; nervous
system of, 850-855.
Mucous membrane, 198-204.
Mucus, 237, 464.

Muscles, contractility of, 345-371; irritability
of, 348-363; tonicity of, 364-366;
rigor mortis of, 367-369; peculiar
force of, 370; heat evolved by,
371; electricity evolved by, 775.
" energy of, dependent on supply of

blood, 358-361.
" disintegration of, 361.
Muscular fibre, striated, 332, 334-339; non-
striated, 333, 337.
Muscular sense, 904. ^

" tissue, 340-344.
Myopia, 958.

N

Nail, 226.

Nervous System, general view of actions of,

840-847.
Nervous System, in Radiata, 849; in Tunic-
ata, 850, 851 ; in Bivalve MoUusca, 852,
853; in higher Mollusca, 853, 854; in Ar-
ticulata, 855-863; in Insects, 856, 857, 861;
in Vertebrata, 867, 868; in Fishes, 869,
870; in Reptiles, 871; in Birds, 872; in
Mammals, 873.
Nervous tissue, 372-405; fibrous, 373-377;
vesicular, 378, 379.
«' " activity of, dependent on

supply of arterial blood,
398-404.
Nucleolus, 250.
Nucleus, 249.
Nutrition, 612-615.

" activity of, dependent on func-

tional activity of parts, 616-
627.

(Esophagus, passage of food along, 455,898.
Oily compounds in food, 430, 432, 435.
Oleine, 261.

Oleo-phosphoric acid, 383.
Olfactive lobes, 869-873, 900.
Olfactory nerve, 946, 947.
Olivary bodies, 891.
Optic lobes, 869-873, 900.
Optic nerves, 910.
Orbit, motor nerves of the, 888.
Osseous tissue, 277-289, 299-309.
Ossification, 300-303.
Otolithee, 950.
Ova of animals, 791-794.
Ovarium, 793-796.
Ovisac, 793, 796.

Oxygen, necessity for, in animal body, 649 ;
mode of introduction of, 650-652.

Pancreatic secretion, 480.

Papilla;, sensory, of skin, 381, 940; of tongue,

943.
Parturition, 827-829.
Par Vagum, 459, 487, 580, 685, 686, 888, 895,

897-899.
Pedal ganglia in Mollusca, 852, 853.

" « in Articulata, 857, 862.
Pepsine, 470, 471.
Perception, nature of, 936, 937.
Perceptions, tactual, 941; visual, 961, 968.
Peristaltic movement, 460.
Perspiration, 743-746.
Peyer's glands, 450.
Phosphate of lime, in food, 438-441.
Phosphatic deposits, 386, 738-740.
Phosphorus, in animal body, 438, 439.
Pigment-cells, 229, 230.
Placenta, structure of, 819, 820.
Placental tufts, 244.

INDEX.

565

Plants, heat of, 762; circulation in, 540-548;

respiration in, 84, 641, 642; reproduction

in, 781-784.
Pneumogastric nerve, see Par Vagum.
Polypes, digestive process in, 443-445.
Posterior Pyramids, 893.
Pregnancy, duration of, 825, 826.
Prehension of food, 896.
Presbyopia, 958.
Primary membrane, 206-209.
Proteine, 168-173.

Puberty, in male, 788; in female, 798.
Pulp of hair, 328, 330.
Pulp of teeth, 310, 313.
Pulsations of heart, 579.
Pulse, in arteries, 583,584; respiratory, in

veins, 607.
Pupil, changes in diameter of, 969.
Pus, 632, 636, 637.
Pyramids, anterior, 890.
« posterior, 893.

R

Radiata, Nervous System of, 849.
Receptaculum Chyli, 497.
Reduction of food, provisions for, 445.
Reflex actions, nature of, 392-396.

« " of Articulata, 858—860; of

Mollusca, 851, 854; of Ver-
tebrata, 875-879.
Repkoduction, general nature of the pro-
cess, 778, 780.
« in Plants, 781-784.

Reproductive cells, 240.
Reptiles, circulation in, 562, 563; lymphatic
system in, 500; respiration in, 668-671;
nervous centres in, 871.
Respiration, nature of the process, 641-642.
" organs of, in lowest animals,

653; in Mollusca, 654-656;
in Annelida, 657 ; in Crusta-
cea, 658; in Insects, 659-
660; in Spiders, 661; in Fish-
es, 663-667; in Reptiles, 668
-671; in Birds, 672-674; in
Mammalia and Man, 675-
688.
** chemical phenomena of, 689-

702.
« insufficient, effects of, 703-709.

Respiratory movements, 680-682; frequency

of, 683.
Respiratory nerves, in Insects, 862 ; in Mol-
lusks, 850-853; in Vertebrata, 684-688,
895.
Respiratory palse, 607.
Restiform bodies, 892.
Retina, general structure of, 960.
Rigor Mortis, 367-369.
Ruminating stomach, 457.

S

Saccharine compounds in food, 430-434, 493.
Salivary glands, 465.

« secretion, 446, 466, 467.

Satiety, sense of, 486.

Sebaceous follicles, 747, 748.

Secreting cells, 238, 239, 712-714.

Secretion, nature of the process, 710-713.
" effects of suppression of, 711.

Selecting power of individual parts, 612-615.

Semicircular canals, 952.

Sensation, 389, 390; nerves of, 389, 391,900,
901; general and special, 932.

Sensations, regulation of muscular movement
by, 904.

Sensorium, 390.

Sensory Ganglia, 900, 901; functions of, 902-
908.

Sensory nerves, 909.

Serous Membranes, 197.

Shell, of Echinodermata, 290,291; of Mol-
lusca, 292-295; of Articulata, 296-298.

Sight, sense of, 955-972.

Single vision with two eyes, 963.

Size of objects, estimate of, 968.

Skin, 198, 204, 742-748, 940.

Sleep, 921.

Smell, sense of, 946-948.

Sneezing, 948.

Solen, nervous system of, 852, 853.

Somnambulism, 923.

Sounds, propagation of, 949; qualities of, 954

Sounds of heart, 571-575.

Speech, 981, 982.

Spermatic fluid, 786, 787; emission of, 790.

Spermatozoa, 240, 787; use of, in fecunda-
tion, 804.

Sphinx ligustri, nervous system of, 856, 857.

Spiders, respiratory organs of, 661.

Spinal Cord, 867, 868; structure of, 880-883;
reflex actions of, 874-879, 884; disordered
states of, 885-887.

Spinal accessory nerve, 580, 888.

Spinal nerves, origin of, 880, 882.
« " peculiar, 888.

Spiracles of Insects, 659.

Spleen, structure of, 506; uses of, 507-509.

Stammering, 983, 984.

Starchy compounds in food, 430-432.

Star-fish, nervous system of, 849.

Stearine, 261.

Stereoscope, 964, 965.

Stomach, 447, 448; movements of, 456-459.
" in Ruminants, 457.

Stomato-gastric nerves of Invertebrata, 863.
" " of Vertebrata, 896.

Strabismus, 963.

Suction, act of, 896.

Sudoriparous glandulsB, 743, 744.

Supra-renal capsules, 510.

Sympathetic System, in Man, ftinctions of,
926-929.
'^ *' traces of, among In-

vertebrata, 864.

Syncope, 581, 628.

Synovial membranes, 197.

T

Tadpole, respiration of, 670 ; metamorphosis

of, 670.
Taste, nerves of, 944.

566

INDEX.

Taste, sense of, 945.

Teeth, structure and development of, 310-327.

Temperature, sense of, 933, 942.

Testis, structure of, 785, 786.

Tetanus, 886.

Thalami Optici, 901.

Thirst, 488.

Thoracic duct, 497.

Thymus Gland, 511.

Thyroid Gland, 613.

Tickling, 907.

Tongue, papillae of, 943.

Tonicity of arteries, 365, 684; of muscle,

364-366.
Torpedo, electricity of, 771-774.
Torpidity, induced by cold, 136; by want of

moisture, 158-161.
Touch, sense of, 939-942.
Tubercula quadrigemina, 873, 900.
Tubercular diathesis, 626, 638, 639.
Tunicata, nervous system of, 850, 851.
Tympanum, 951.

U

Ulceration, 635.
Urea, 730, 731.
Uric acid, 732, 733.

Urine, composition and properties of, 729-
741; effects of suppression of, 741.

Vascular area, 551, 813, 814.

Vegetation, influence of light upon, 79-92;

influence of Heat upon, 98-107.
Veins, movement of blood in, 605-610.
Venous congestion, 609, 610.
Villi of mucous membrane, 241, 242.
Vitreous body of eye, 276.
Vocal ligaments, 974-979.
Voice, production of, 973-979.
Vowel sounds, production of, 981.

W

Waste or disintegration of tissues, 361, 384,

617.
White fibrous tissue, 189, 190.
Worm tribes, circulation in, 552; respiration

in, 657.

Yellow fibrous tissue, 189, 192.
Zona pellucida, 802.

THE END.

LEA AND BLANCHARD
Publish the following Valuable Works

BY DR. CARPENTER.

ELEMENTS OF PHYSIOLOGY,

INCLUDING

PHYSIOLOGICAL ANATOMY,

FOR THE USE OF THE MEDICAL STUDENT.

With One Hundred and Eighty Illustrations.
By W. B. CARPENTER, M.D., F.R.S.,

Lecturer on Physiology to the Bristol Medical School, &c. &c.
In one very neat Octavo Volume.

A POPULAR TREATISE

ON

VEGETABLE PHYSIOLOGY

By W. B. CARPENTER, M. D., F.R.S., &c.

Published under the Auspices of the Society for the Promotion of Popular Instruction.
In one neat duodecimo Volume, Extra Clothj

WITH NUMEROUS ILLUSTRATIONS.

Lea and Blanchard will publish the

POPULAR CYCLOP/EDIA OF NATURAL SCIENCE,

BY DR. CARPENTER,
OF WHICH THE VEGETABLE PHYSIOLOGY FORMS A PART.

(In press.)

PRINCIPLES

OF

GENERAL AND COMPARATIVE PHYSIOLOGY,

Intended as an Introduction to the Study of Human Physiology and as a

Guide to the Philosophical Pursuit of Natural History.

BY W. B. CARPENTER, M. D., F. R. S., &c. &c.

FROM THE SECOND LONHON EDITION.

With Alterations and Further Improvements by the Author.

IN ONE VERY NEAT OCTAVO VOLUME.

With Numerous Illustrations, Beautifully Executed on Stone.

*'This is an admirable work, and will give Dr. Carpenter a high rank among the cultiva-
tors of Natural Philosophy. We strongly recommend it to all who have leisure for the
delightful subject of which it treats." — Medical Gazette.

" There are very few persons in Great Britain who could have undertaken, with any
prospect of success, the execution of a plan requiring such varied and, at the same time,
such accurate knowledge. It is difficult to decide in what department Dr. Carpenter dis-
plays most research, for in each he appears as though that alone had engaged his exclusive
attention. In fact, a work displaying so much erudition and so much knowledge derived
from actual observation, we have not met with in any young English Writer of the present
day. The volume contains just so much of each subject as it actually deserves, considered
not by itself in an insulated manner, but as a part of a great and systematic whole." —
Dublin Medical and Surgical Journal.

A xNEW EDITION OF

CARPENTER'S HUMAN PHYSIOLOGY,

REVISED AND BinCH IMPROVED.

PRINCIPLES OF HUMAN PHYSIOLOGY,

WITH THEIR CHIEF APPLICATIONS TO

PATHOLOGY, HYGIENE, AND FORENSIC MEDICINE.
BY WILLIAM B. CARPENTER, M.D., F.R.S., &c.

SECOND AMERICAN, FROM A NEW AND REVISED LONDON EDITION.

WITH NOTES AND ADDITIONS,

BY MEREDITH CLYMER, M.D., &c.

With Two Hundred and Sixteen Wood-cut and other Illustrations.
In one octavo volume, of about 650 closely and beautifully printed pages.

The very rapid sale of a large impression of the first edition is an evidence of the merits of this
valuable work, and that it has been duly appreciated by the profession of this country. The publish-
ers hope that the present edition will be found still more worthy of approbation, not only from the ad-
ditions of the author and editor, but also from its superior execution, and the abundance of its illustra-
tions. No less than eighty-five wood -cuts and another lithographic plate will be found to have been
added, affording the most material assistance to the student.

" We have much satisfaction in declaring our opinion that this work is the best systematic treatise
on physiology in our own language, and the best adapted for the student existing in any language." —
Medico-Chirurgical Review.

"This work as it now stands is the only Treatise on Physiology in the English language which ex-
hibits a clear and connected, and comprehensive view of the present condition of that science.

" Few individuals could have been found so well qualified as Dr. Carpenter for acting as the histo-
rian of physiological science. He is endowed with great perseverance and industry, possesses a clear
and logical judgment, is able to see distinctly the salient points of the more abstruse and disputed doc-
trines, has excellent powers of generalization, and can express his thoughts in lucid and correct lan-
guage. In explaining the general doctrines of the science, or in describuig the phenomena attending
the performance of individual functions, he lays before the reader a judicious admixture of the most
trustworthy facts, with the inductions to which they lead, which cannot fail to give him a clear con-
ception of each subject brought under his notice. When he ventures upon any new generalizations,
he never indulges in dogmatical and bold assertions, but proceeds in a cautious and philosophical
spirit; this cannot fail to exercise a salutary influence upon the mind of the student by repressing that
tendency to hypothetical speculation to which young and ardent minds are so prone. He omits no op-
portunity of pointing out how the physiological facts and doctrines he is discussing may be employed
in furnishing more scientific methods of treating disease.^'— The London^ Edinburgh Monthly Journal
of Medical Sciences.

"This work exhibits all the mental characteristics of Dr. Carpenter; great knowledge of what has
been done by others, clearness of conception, and lucidness of arrangement. Although entitled
' Human Physiology,' many of its details are on Histology and Histogeny, or the minute anatomy^ and
development of tissues which man possesses in common with the rest of the animated creation. They,
however, who are fond of such investigations, and who is there who is not more or less so, will find
the transcendental as well as the more sober views of modern inquiries well depicted.^'''— Am. Medical
Library.

"Though the resources of the author's comprehensive mind are apparently devoted to the advance-
ment of new beginners in study, there is a splendid exhibition of the powers of analysis, an uncommon
degree of success in making abstruse objects clear, and in forcibly impressing upon others the laws of
life wKich he so well understands, which will give eclat to Dr. Carpenter's reputation when he will be
insensible to praise. All who can afford to have a good system of physiology should possess this; and
those who are able to keep pace with the progress of science should not be without it. There are 618
pages, large sized octavo, on good paper, with a type as distinctly made as it can be executed. No
necessity seems to exist for extracting from its pages, or commenting especially on any particular parts
or portions of the volume, because it is presumed that all who can will avail themselves of it. Proba-
bly this improved edition does not cost more than one-third the price asked for it in England, and yet
jt rs superior in very many respects."— ^osion, Med. ^ Surg. Journal.

"It would be a dereliction ofour bibliographical duty not specially to mention the highly meritorious
work of Dr. Carpenter on the Principles of Human Physiology, a work to which there has been none
published of equal value in the department of which it treats, embodying, as it does, an immense store
of facts and modern discoveries in anatomy and physiology down to the present time."— Dr. .B/ac^'s
Retrospective Address.

" It is a clear compendious r^sumfe of the existing state of Physiological Science, conceived and ex-
ecuted in a genuine philosophical spirit, and peculiarly adapted to the medical student. All the received
facts of physiology are presented in a well digested form and lucid manner, and the deductions made
from them show close reasoning, and a very impartial spirit. The author, though still a young man,
has already won a high reputation in this department of medicine. In a literary point of view, the
present work, as well as his other productions, are of a high order; his style is clear precise, and un-
ostentatious, at times rising to positive elegance."— Jllec/. E.mminer.

CATALOGUE

OP

MEDICAL, SURGICAL

SCIENTIFIC,
AND

MISCELLANEOUS

BOOKS,

PUBLISHED BY

LEA AND BLANCHARD,

PHILADELPHIA.
1847.

MISCELLANEOUS WORKS

PUBLISHED BY

LEA AND BLANCHARD.

Acton's Modern Cookery, 420 large pages,
with many cuts, 12mo., neat extra cloth.

American Ornithology, by Prince Charles
Bonaparte, in 4 vols, folio, half bound, many
colored plates.

American Military Law, by Lieut. O'Brien,
U. S. A., 1 vol. 8vo., cloth or law^ sheep.

Addison on Contracts, at press.

Arnott's Elements of Physics, new edition,
I vol. 8vo., sheep, many cuts.

Boz's Complete Works, 8 parts, paper, cheap-
pst edition, containing Pickwick, 50 cents;
Sketches, 37^ cents ; Oliver Twist, 25 cents;
Nickleby, 50 cents ; Curiosity Shop, 50 cents ;
Barnaby Rudge, 50 cts. ; Martin Chuzzlewit,
50cts. ; and Christmas Stories and Pictures
from Italy, 37 J cts.-Any work sold separately.

Boz's Works, in 3 large vols., extra cloth, good
paper, price $3.75. — N. B. A fourth vol. is
preparing, to contain Dombey & Son, Christ-
mas Stories, and Pictures from Italy.

Boz's Works, in 8 vols., imperial 8vo., extra
oloth, with 136 plates and 140 cuts.

Bi:nthamiana : Extracts from Bentham, in one
large vol., ISmo.

Browne's Religio Medici, and Christian Mo-
rals, 1 vol., 12mo., extra cloth.

Bolmar's French Series, consisting of— A Se-
lection of One flundred Perrin's Fables, with
a Key to the Pronuncintion ; a Series of Collo-
quial Phrases ; The First Eight Books of Fe-
nelon's Telemachus ; Key to the same; a
Treatise on all the French Verbs, Regular and
Irregular. The whole forming five small vol-
umes, half bound to match.

Butlkr's Atlas of Ancient Geogr/vphy, with
an Accentuated Index, 8vo., half bound, 27
colored maps.

Butler's Geographia Classica, 1 vol., 8vo.

Brigham on Mental Excitement and Culti-
vation, &c., 12mo., cloth.

BrRD's Natural Philosophy, I vol., 12mo.,
many cuts, [at pr^ ss.]

B ridgewater Treatises. — The whole complete
in 7 vols., 8vo., various bindings.

Brougham's Historical Sketches of States-
men, 3d Series, 1 vol., 12mo., cloth.

Barnaby Rudge, by " Boz," paper or cloth.

Browning's History of the Huguenots, one
vol., 8vo., cloth.

Bkewster's Treatise on Optics, I vol., 12mo.,
cuts.

Buckland's Geology, 2 vols., 8vo., cloth, many
plates.

Tomplete Cook, paper, price only 25 cents.

Complete Confectioner, paper, price 25 cents.

Complete Florist, paper, 25 cents.

Complete Gardene.**. do. do.

Campbell's (Lord) Lives of the Lord Chan-
cellors of England, in Sv^ls. neat demy 8vo.

Second and concluding series, 3 vols.8vo. at press.

Curiosity Shop, by " Boz," paper or cloth.

Christmas Stories, containing the Chimes, the

Carol, the Cricket on the Hearth, and The

Battle of Life ; together with Pictures from

Italy, By " Boz." Neat 8vo., price 31i cts.

(2)

Campbell's Complete Poetical Works, Id

one vol., crown 8vo., cloth gilt or white calf,

plates.
Cooper's Naval History of the United

States.
Cooper's Novels and Tales, in 23 vols., sheep

gilt, 12mo., or 47 vols., paper, price 25 cents

per vol.
Cooper's Sea Tales, 6 large vols., royal 12mo.,

extra cloth.
Cooper's Leather Stocking Tales, 5 large

royal 12mo, vols., extra cloth.
Clater's Horse Doctor, I vol., 12mo. cloth.
Clater's Cattle and Sheep Doctor, one v«)l.,

12mo., cuts.
Carpenter's Popular Vegetable Physiolog y,

1 vol., 12mo., extra cloth, many cuts.
Carpenter's Comparative Physiology, one

vol., large 8vo., many plates, [preparing.]
Carpenter's Elements of Physiology, one

vol., 8vo., with many cuts.
Dana on Corals, &c., 1 vol. imp. quarto, with

an Atlas of colored plates, being vols. 8 and 9

of the U. S. Exploring Expedition, [preparing] .
Davidson, Margaret, Memoirs of and Poems,

in 1 vol., 12mo., paper 50 cents, or extra cloth.
Davidson, Lucretia, Poetical Remains, 1

vol., 12mo., paper 50 cents, or extra cloth.
Davidson, Mrs., Poetry and Life, in 1 vol.,

12mo., paper 50 cents, or extra cloth.
Dombey & Son, by Dickens, to be complete in

20 Nos., with 2 plates each ; price 8 cts. each.
Dog and Sportsman, by Skinner, plates, 1 vol.,

12mo., cloth.
Dunglison on Human Health, 1 vol., Svo.,

cloth or sheep.
Encyclopedia of Geography, in 3 vols., 8vo.,

many cuts, various bindings.
EncyclopjEdia Americana, 14vo1s. 8vo., various

bindings. The supplementary volume (14th),

by Professor Henry Vethake, is just published.

To be had separate, price $2.00 uncut in cloth,

or $2.50 bound.
East's Reports, edited by G. M. Wharton, in

8 vols., large 8vo,, law sheep.
Education of Mothers, 1 vol., 12mo., cloth or

paper.
Electro-Magnetic Telegraph, by Vail, 8vo.,

sewed, many cuts.
Frederic the Great, by Campbell, 2 vols.,

12mo., extra cloth.
Fielding's Select Works, in 1 vol. large 8vo.,

cloth, or in 4 parts paper, price $1.25.
Francatelli's Modern French Cook, in 1

vol., 8vo., fancy cloth, with many cuts.
Fownes' Elementary Work on Chemistry,

1 vol., 12mo., many cuts, cloth or sheep.
Grahame's Colonial History of the United

States, 2 vols., 8vo., a new edition.
Grote's History of Greece, 8vo., cloth, [pre-
paring.]
Giesler's Ecclesiastical History, 3 vols. Svo.
Griffith's Chemistry of the Four Seasons,

1 vol., 12mo., extra cloth, cuts.
Hawker on Shooting, Edited by Porter, one

beautiful 8vo. vol., rich extra cloth, plates.

MISCELLANEOUS WORKS PUBLISHED BY LEA AND BLANCHARD.

Hale's Ethnography and Philology, impe-
rial 4to., being 7th vol. of the U. S. Exploring
Expedition.

Herschell's Treatise on Astronomy, 1 vol.,
12mo., cuts.

Hemans' Complete Poetical Works, in 7
vols., I2nio.

Hemans' Memoirs, by her Sister, 1 vol., 12mo.,
cloth.

HiLLlARD ON THE AMERICAN LaW OF ReAL

Estate, 2 large vols., 8vo., law sheep.
Hill on Trustees, Edited by Troubat, 1 large

vol., 8vo., law sheep.
Holthouse's Law Dictionary, with large ad-
ditions, 1 vol., royal 12mo.
Tngersoll's History of the Late War, 1 vol.,

Svo.
Irving's Columbus, in 2 vols., Svo.
Irving's Beauties, in 1 vol., 18mo.
Irving's Rocky Moujvtains, 2 vols., 12mo.,

cloth.
Johnson's Gardener's Dictionary, edited by

Landreth, 1 vol., large 12mo., with cuts.
Keble's Christian Year, in 32mo., extra

cloth, with illuminated title.
KiRBY ON Animals, 1 vol., 8vo., plates.
KiRBY AND Si'ence's Entomology, 1 large Svo.

vol., with plates, plain or colored.
Life of Thomas Jefferson, by Judge Tucker,

2 vols., 8vo.
Language of Flowers, 1 vol , ISmo., colored

plates, extra crimson cloth, gilt.
Loves of the Poets, by Mrs. Jainieson, 12mo.
Landreth's Rural Register, for 1847, royal

12mo. ; price only 15 cts., about 100 cuts.
Lover's Rory O'More, royal 12mo., wUh cuts,

paper, price 50 cts., or extra green cloth.
Lover's Legends and Stories of Ireland,

royal 12mo., with cuts, paper, price 50 cts.,
. or in extra green cloth.
Lover's Songs and Ballads, royal 12mo.,

paper, price 25 cts.
Marston; or the Soldier and Statesman, by

Croly, Svo., sewed, 50 cts.
Mackintosh's Ethical Philosophy, ! vol.,

Svo.
Medical Botany, by R. E. Griffith, M. D.,

with 400 illustrations.
Moore's History of Ireland, complete in 2

vols., Svo., cloth.
Martin Chuzzlewit, by ' 'Boz," cloth or paper.
Millwright's and Miller's Guide, by Oli-
ver Evans, 1 vol. Svo., many plates, new ed.
Mills' History of the Crusades and Chi-
valry, 1 vol., 8vo., extra cloth.
Mills' Sportsman's Library, 1 vol., 12mo.,

extra cloth.
Narrative of the United States Exploring

Expedition, by Captain Charles Wilkes, U.

S. N. In 6 vols., 4to., 860; or 6 vols. imp.

Svo., $25 ; or 5 vols. Svo., $10.
Niebuhr's History of Rome, complete, 2 vols.

Svo., extra cloth.
Nicholas Nickleby, by "Boz," cloth or paper.
Oliver Twist, by "Boz," cloth or paper.
PiccioLA, — The Prisoner op Fenestrella,

12mo., illustrated edition.
Pickwick Club, by "Boz," cloth or paper.
Philosophy in Sport made Science in Ear-
nest, 1vol. royal 16mo., whh many cuts.

Rush s Residence at the Court of London,
new series, 1 neat vol., Svo., cloth.

Ranke's History of the Popes of Rome, 1
vol., Svo., cloih.

Ranke's History of the Reformation in
Germany, to be complete in one vol., Svo.

Ranke's History of the Ottoman and Span-
ish Empires.

Rogers' Poems, a splendid edition, illustrated,
imperial 8vo., extra cloth.

Roget's Outlines of Physiology, one vol.,
Svo.

Roget's Animal and Vegetable Physiology,
2 vols., Svo., cloth, with about 400 wood-
cuts.

Roscoe's Lives of the Kings of England, a
12mo. series to match the Queens. Vol. 1
now ready.

Strickland's Lives of the Queens of Eno-
LAND, 9 vols., 12mo., cloth or paper, [to be
continued.]

Select Works of Tobias Smollett, 1 vol.,
large Svo., cloth, or 5 parts, paper, $1.50.

Siborne's Waterloo Campaign, with Maps

1 vol., largo Svo.

Stable Talk and Table Talk, for Sports-
men, 1 vol., 12mo.

Small Books on Great Subjects — No. 1, "Phi-
losophical Theories and Philosophical
Experience." No. 2, "On the Connection
•lETWEEN Physiology and IntellectuaIj
Science." No. 3, "On Man's Power over
himself to prevent or control insanity."
No. 4, "An Introduction to Practical
Organic Chemistry." No. 5, "A Brief
View of Greek Philosophy up to the Age
OF Pericles." No. 6, "A Brief View of
Greek Philosophy from the Age of So-
crates TO the Coming of Christ." No. 7,
"Christian Doctrine and Practice in the
Second Century." No. S, "An Exposi-
tion OF Vulgar and Common Errors,

ADAPTED TO THE YeAR OF GrACE 1845." No.

i>, "An LvTuoDrcTioN to Vegetable Phy-
siology, WITH References to the Works
of De Candolle, Lindley, &c." No. 10,
"On the Principles of Crijiinal Law."
No. 11, "Christian Sects in the Nine-
teenth Century." No. 12, "Principles of
Grammar," &c. — Each work separate 25 cts.,
or handsomely done up in 3 volumes, in cloth,
luruiiiig a neat series. (To be continued.)

Spence on the Jurisdiction of the Court of
(/iJANiERV, 1 vol., large Svo., law sheep.
Vol. 2, on the Practice, preparing.

Thomson's Domestic Management of the
Sick Room, 1 vol., 12mo., extra cloth.

ToKEAH, by Sealsfield, price 25 cents.

Trimmer's Geology and Mineralogy, one
volume of large Svo., extra cloth, many cuts.

Walpole's Letters, in 4 large vols., Svo.,
extra cloth, with a portrait.

Walpole's New Letters to Sir Horace
Mann, 2 vols., Svo., extra cloth.

Walpole's Memoirs of George the Third,

2 vols., Svo., extra cloth.

Sir George Simpson's Voyage round the
World, 1 vol., demy Svo.

White's Universal History, a new and im-
proved work for schools, colleges, &c., with
Questions, by Professor Hart, in 1 vol., large
12mo., extra cloth, or half bound.

Wiieaton's Elements OF International Law,
1 vol., large Svo., law sheep or extra cloth,
third edition, much improved.

Wraxall's Posthumous Memoirs, 1 vol.,
Svo., extra cloth.

Wraxall's Historical Memoirs, 1 vol., Svo.,
extra cloth.

YouATT ON the Horse, &c., by Skinner, 1
vol., Svo., many cuts.

YouATT ON the Dog, in one beautiful volume,
crown Svo., extra cloth, with plates.

TO THE MEDICAL PROFESSION.

The following list embraces works on Medical and other Sciences issued by the subscrib-
ers. They are to be met wiih at all the principal bookstores throughout the Union, and will
be found as low in price as is consistent with the correctness of their printing, beauty of exe-
cution, illustration and durability of binding. No prices are here mentioned, there being no
fixed standard, as it is evident that books cannot be retailed at the same rate in New Orleans
or Chicago as in Philadelphia. Any information, however, relative to size, cost, &c., can
be had on applicatioR, free of postage, to the subscribers, or to any of the medical book-
sellers throughout the country.

I.EA & BtAXCHARD, Philadelphia.

DICTIONARIES AND JOURNALS.
American Journal of the Medical Sciences, quar-
terly, at $5 a year.
Cyclopaedia of Practical Medicine, by Forbes,
Tweedie, &c., edited by Dunglison, in 4 super
royal volumes, 3154 double columned pages.
Dunglison's Medical Dictionary, 6th ed., 1 vol.
imp.8vo.,804 large pages, double columns.
Hoblyn's Dictionary of Medical Terms, by Hays,
1 vol. large 12mo., 402 pages, double columns.
Medical News and Library, monthly at $1 a year.

ANATOMY.
Anatomical Atlas, by Smith and Horner, large

imp. 8vo., 650 figures.
Horner's Special Anatomy and Histology, 7th

edition, 2 vols. 8vo., many cuts, 1130 pages.
Horner's United States Dissector, 1 vol. large

royal 12mo., many cuts, 444 pages.
Wilson's Human Anatomy, by Goddard, 3d edi-
tion, I vol. 8vo., 235 wood-cuts, 620 pages.
Wilson's Dissector, or Practical and Surgical
Anatomy, with cuts, 1 vol. 12mo., 444 pages.
PHYSIOLOGY.
Carpenter's Principles of Human Physiology, 1

vol. 8vo., 644 pages, many cuts, 2d edition.
Carpenter's Elements, or Manual of Physiology,

1 vol. 8vo., 666 pages, many cuts.
Connection between Physiology and Intellectual
Science, 1 vol. 18mo., paper, price 25 cents.
Dunglison's Human Physiology, 6th edition, 2

vols. 8vo., 1350 pages, and 370 wood-cuts.
Harrison on the Nerves, 1 vol. 8vo., 292 pages.
MUller's Physiology, by Bell, I vol. 8vo.,886pp.
Roget's Outlines of Physiology, 8vo., 516 pages.
Todd and Bowman's Physiological Anatomy and
Physiology of Man, with numerous wood-cuts.
(Publishing in the Medical News.)
PATHOLOGY.
Andral on the Blood, I vol, small 8vo., 120 pages.
Abercrombie on the Stomach, new edition, 1 vol.

8vo., 320 pages.
Abercrombie on the Brain, new edition, 1 vol.

8vo., 324 pages.
Alison's Outlines of Pathology, &c., 1 vol. 8vo.,

420 pages.
Berzelius on the Kidneys and Urine, 8vo., 180 pp.
Bennet on the Uterus, 1 vol. 12mo., 146 pages.
Budd on the Liver, 1 vol. 8vo., 392 pages, plates

and wood-cuts.
Billing's Principles, 1 vol. 8vo., 304 pages.
Bird on Urinary Deposits, 8vo., 228 pages, cuts.
Hasse's Pathological Anatomy, 8vo., 379 pages.
Hope on the Heart, by Pennock, a new edition,

with plates, 1 vol. 8vo., 572 pages.
Hughes on the Lungs and Heart, 1 vol. 12mo.,

270 pages, with a plate.
Philip on Protracted Indigestion, 8vo., 240 pp.
Philips on Scrofula, 1 vol. 8vo., 350 pages.
Prout on the Stomach and Renal Diseases, 1 vol.

8vo., 466 pages, colored plates.
Ricord on Venereal, new ed., 1 vol. 8vo,, 256 pp.
Vogel's Pathological Anatomy of the Human
Body, 1 vol. 8vo., 536 pages, col. plates.

Walshe on the Lungs, 1 vol. 12mo., 310 pages.
Wilson on the Skin, 1 vol. Svo., 370 pages.
Williams' Pathology, or Principles of Medicine,

1 vol. 8vo., 384 pages.
Williams on the Respiratory Organs, by Clyraer,

1 vol. 8vo., 500 pages.

PRACTICE OF MEDICINE.
Ashwell on the Diseases of Females, by Goddard,

1 vol. 8vo., 520 pages.
Benedict's Compendium of Chapman's Lectures,

1 vol. 8vo., 258 pages.
Chapman on Thoracic and Abdominal Viscera,

&c., 1 vol. 8vo., 384 pages.
Chapman on Fevers, Gout, Dropsy, &c. &c., 1 vol,

8vo., 450 pages.
Colombat do L'Isbre on Females, translated and

edited by Meigs, 1 vol. Svo. , 720 pages, cuts.
Condie on the Diseases of Children, 2d edition, I

vol. 8vo., 658 pages.
Churchill on the Diseases of Females, by Huston,

4lh edition, 1 vol. 8vo., 604 pages.
Clymer and others on Fevers, a complete work

in 1 vol. Svo. 600 pages.
Dewees on Children, 9th ed., 1 vol. 8vo., 548 pp.
Dewees on Females, 8th edition, 1 vol.Svo., 532

pages, with plates.
Dunglison's Practice of Medicine, 2d edition, 2

vols. 8vo., 1322 pages.
Esquirol on Insanity, by Hunt, Svo. 496 pages.
Thomson on the Sick Room, &c., 1 vol. large

12mo., 360 pages, cuts.
Watson's Principles and Practice of Physic, 2d

edition by Condie, 1 vol. 8vo., 1060 large pages.

SURGERY.

Brodie on Urinary Organs, 1 vol. Svo. , 214 pages.

Brodie on the Joints, 1 vol. Svo. 216 pages.

Brodie's Lectures on Surgery, 1 vol. 8vo., 350 pp.

Chelius' System of Surgery, by South and Norris,
in 3 large Svo. vols., near 2000 pages, or in 17
parts at 50 cents each.

Cooper on Dislocations, and Fractures, 1 vol. Svo.
500 pages, many cuts.

Cooper on Hernia, 1 vol. imp. 8vo,, 428 pp., pl'ts.

Cooper on the Testis and Thymus Gland, 1 vol.
imperial Svo. many plates.

Cooper on the Anatomy and Diseases ofthe Breast,
Surgical Papers, &c. &c., I vol. imp. 8vo., pl'ts.

Druitt's Principles and Practice of Modern Sur-
gery, 3d ed., 1 vol. Svo. ,534 pages, many cuts.

Durlacher on Corns, Bunions, &c. 12mo., 134 pp.

Fergusson's Practical Surgery, 1 vol. 8vo., 2d
edition, 640 pages, many cuts.

Guthrie on the Bladder, Svo., 150 pages.

Harris on the Maxillary Sinus, Svo., 166 pp.

Jones' (Wharton) Ophthalmic Medicine and Sur-
gery, by Hays, 1 vol. royal 12mo.,529 pages,
many cuts, and plates plain or colored.

Liston's Lectures on Surgery, by MUtter, 1 vol.
Svo., 566 pages, many cuts.

Lawrence on the Eye, by Hays, new edition,
much improved, 863 pages, many cuts & plates.

Lawrence on Ruptures, 1 vol. Svo. 480 pages.

Miller's Principles of Surgery, 1 vol. Svo., 526 pp.

LEA & BLANCHARD'S PUBLICATIONS.

Miller's Practice of Surgery, 1 vol. 8vo., 496 pp.
Maury's Dental Surgery, 1 vol. 8vo., 286 pages,

many plates and cuts.
Robertson on the Teeth, 1 vol. 8vo., 230 pp. pts.

MATERIA MEDICA AND THERAPEUTICS.
Dunglison's Materia Medica and Therapeutics, a

new ed., with cuts, 2 vols. 8vo., 986 pages.
Dunglison on New Remedies, 5th ed., I vol.Svo.,

653 pages.
Ellis' Medical Formulary, 8th ed., much improv-
ed, 1 vol. 8vo., 272 pages.
Griffith's Medical Botany, a new work, 1 large

vol. 8vo., with over 350 illustrations.
Pereira's Materia Medica and Therapeutics, by

Carson, 2d edition, 2 vols. Svo., 1580 very

large pages, nearly 300 wood-cuts.
Royle's Materia Medica and Therapeutics, by

Carson, 1 vol. 8vo., 689 pages, many cuts.

OBSTETRICS.

Churchill's Theory and Practice of Midwifery, by

Huston, 2d ed,, 1 vol. 8vo., 520 pp., many cuts.
Dewees' System of Midwifery, lith ed., 1 vol.

Svo. 660 pages, with plates.
Rigby's System of Midwifery, 1 vol. Svo. 492 pp.
Ramsbotham on Parturition, with many plates, 1

large vol. imperial 8vo., new and improved

edition, 520 pages.

CHEMISTRY AND HYGIENE.
Brighamon Excitement, &c., 1 vol. 12mo., 204 pp.
Dunglison on Human Health, 2d ed.,8vo., 464 pp.
Fowne's Elementary Chemistry for Students, 1

vol. royal 12mo., 460 large pages, many cuts.
Graham's Elements of Chemistry, I vol. 8vo., 750

pages, many cuts.
Griffith's Chemistry of the Four Seasons, 1 vol.

royal 12mo., 451 pages, many cuts.
Practical Organic Chemistry, 18mo., paper, 25 cts.
Simon's Chemistry of Man, 8vo., 730 pp., plates.

MEDICAL JURISPRUDENCE, EDUCATION,

&c.
Bartlett's Philosophy of Medicine, 1 vol. 8vo.,
312 pages.

Dunglison's Medical Student, 2d ed.l2mo., 312 pp.
Man's Power over himself to Prevent or Control

Insanity, ISnio. paper, price 25 cents.
Taylor's Medical Jurisprudence, by Griffith, 1

vol. 8vo., 540 pages.
Traill'sMedical Jurisprudence,! vol.Svo. 234pp.

NATURAL SCIENCE, &c.
Arnott's Elements of Physics, new edition, 1 vol.

8vo., 484 pages, many cuts.
Brewster's Treatise on Optics, I vol. 12mo., 423

pages, many cuts.
Babbage's " Fragment," 1 vol. 8vo., 250 pages.
Buckland's Geology and Mineralogy, 2 vols. 8vo.,

with numerous plates and maps.
Bridgewater Treatises, with many plates, cuts,

maps, &c., 7 vols. 8vo., 3287 pages.
Carpenter's Popular Vegetable Physiology, 1 vol.

royal 12mo., many cuts.
Hale's Ethnography and Philology of the U. S.

Exploring Expedition, in 1 large imp. 4to. vol.
HerschelTs Treatise on Astronomy, 1 vol. 12mo.

417 pages, numerous plates and cuts.
Introduction to Vegetable Physiology, founded

on the works of De Candolie, Lindley, &c.,

ISmo., paper, 25 cents.
Kirby on Animals, plates, 1 vol.Svo., 520 pages.
Kirby and Spence's Entomology, from 6th Lon-
don ed., 1 vol. 8vo., 600 large pages; plates,

plain or colored.
Philosophy in Sport made Science in Earnest, 1

vol. royal 18mo., 430 pages, many cuts.
Roget's Animal and Vegetable Physiology, with

400 cuts, 2 vols. Svo., 872 pages. ^
Trimmer's Geology and Mineralogy, 1 vol. Svo.,

528 pages, many cuts.

VETERINARY MEDICINE.
Claterand Skinner's Farrier, 1 vol. 12mo.,220 pp.
Youatt's Great Work on the Horse, by Skinner,

1 vol. 8vo., 448 pages, many cuts.
Youatt and Clater's Cattle Doctor, 1 vol. 12mo.,

282 pages, cuts.
Youatt on the Dog, by Lewis, 1 vol. demy 8vo.,

403 pages, beautiful plates.

XE"W MEDICAIi AMD SCIENTIFIC BOOKS.

Lea Sf Blanchard have at press and preparing for publication thefoUowing works.

Carpenter's Comparative Anatomy and Physiology, revised by the author, with beautiful steel plates.

A New Work on the Diseases and Surgery of the Ear, with illustrations.

Bird's Natural Philosophy, from a new Lond. ed., in 1 vol. royal 12mo. with wood-cuts.

Youatt on the Pig, a new work with beautiful illustrations of all the different varieties.

Maunder's Treasury of Natural History, a Popular Dictionary of Animated Nature, with illustrations.

Dana on Corals, imp. 4to,, with an Atlas of Maps, being vols. 8 and 9 of the U. S. Ex. Expedition.

Churchill on the Management and more Important Diseases of Infancy and Childhood, in 1 vol. Svo.

Solly on the Human Brain, its Structure, Physiology and Diseases.

SpooNER on Sheep, with numerous wood-cuts.

Malgaigne's Operative Surgery, with numerous wood-cuts.

QuAiN's Elements of Anatomy, by Dr. Sharpey, with many illustrations.

De La Beche's new work on Geology, with numerous wood-cuts.

SouTHWooD Smith's Philosophy of Health.

Kane's Elements of Pharmacy, with additions, in 1 vol. 12mo.

The Universal Formulary and Pharmacy, by R. E. Griffith, M. D., in 1 vol. Svo.

An Analytical Compend of the Various Branches of Practical Medicine, Surgery Anatomy, Mid-
wifery, Diseases of Women and Children, MateriaMedica and Therapeutics, Physiology, Chemistry
and Pharmacy, by John Neill, M. D., and F, Gurney Smith, M. D., with numerous illustrations.

Taylor's Manual of Toxicology, in 1 vol. Metcalf on Caloric, in one large Svo. volume.

The History, Diagnosis and Treatment of Typhoid, Typhus, Bilious Remittent, Congestive and
Yellow Fever, by Elisha Bartlett, M. D., &c., being a new and extended ed. of his former work.

A Cyclopedia of Anatomy and Physiology, based on the large work of Todd, in 2 vols, large Svo.

The Universal Dispensatory, with many wood-cuts, in 1 large Svo. volume.

A New Work on Bandaging, and other Points of Minor Surgery, in 1 vol. 12mo., with wood-cuts.

Elements of General Therapeutics, &c., by Alfred Stillfe, M.D., in 1 vol. Svo.

CoATES' Popular Medicine, a new edition, fully revised and brought up, in 1 vol. large 12mo.

Professor Meigs' New Work on Females ; their Diseases and their Remedies, in a Series of Let*
ters to his Class, in I vol. Svo.

Together with various other works.

LEA & BLANCHARD'S PUBLICATIONS.

NOW OOMPLEIE.

THE GREAT SURGICAL LIBRARY.

A SYSTEM "OF SURGERY.

BY J. M. CHELIUS,

Doctor in Medicine and Surgery, Public Professor of General and Ophthalmic Surgery, etc. etc. in the Uni-
versity of Heidelberg.

TRANSLATED FROM THE GERMAN,

AND ACCOMPANIED WITH ADDITIONAL NOTES AND OBSERVATIONS,
BY JOHN F. SOUTH,

Surgeon to St. Thomas' Hospital.
EDITED, WITH REFERENCE TO AMERICAN AUTHORITIES,
BY GEORGE W. NORRIS, M. D.
Now complete in three large octavo volumes of over six hundred pages each, or in 17 numbers, at fifty cents.
This work has been delayed beyond the time originally promised for its completion, by the very extensive
additions of the translator. In answer to numerous inquiries, the publishers now have the pleasure to pre-
sent it in a perfect state to the profession, forming three unusually large volumes, bound in the best manner,
and sold at a very low price.

This excellent work was originally published in Germany, under the unpretending title of "Handbook to
the Author's Lectures." In passing, however, through six successive editions, it has gradually increased
in exlent and importance, until it now presents a complete view of European Surgery in general, but more
especially of English practice, and it is acknowledged to be well fitted to supply the admitted want of a com-
plete and extended system of Surgery in all its branches, comprehending both the principles and the prac-
tice of this important branch of the healing art. Since Benjamin Bell's great work, first published in 1783,
and now almost obsolete, no thorough and extended work has appeared in the English language, occupying
the ground which this is so well calculated to cover.

The fact of this work being carried to six editions in Germany, and translated into no less than eight lan-
guages, is a sufficient evidence of the ability with which the author has carried out his arduous design.

This translation has been undertaken with the concurrence and sanction of Professor Chelius. The trans-
lator, Mr. John F. South, appears 1o have devoted himself to it with singular industry and ardor, and to have
brought it up almost to the very hour of publication His notes and additions are very numerous, embodying
the results and opinions of all the distinguished surgeon^ of the day, Continental, English and American.
The leading opinions of .John Hunter, on which Modern English Surgery has been raised, are set forth ; the
results of the recent microscopical discoveries, esi)ecially in reference to infiammaiion, will be found here,
together with many other practical observations, placing the work on a level with the present slate of Sur-
gery, and rendering it peculiarly useiul, both to the student and practitioner.

The labors of the English translator have been so numerous and important, that there is but little which
remains to be supplied by the American editor. Dr. G. W. Norris has consented, howeverj to superintend
the passage of the workj through the press, and supply whatever may have been omitted in relation to the
Surgical Literature oflhis country.

The Medical Press and profession, both in England and in this country, have joined ia
praise of this great work, as being more complete than any other, and as affording a compiete
library of reference, equally suited to the practitioner and to the student.

" We strongly recommend all surgical practitioners and students, who have not yet looked into this work,
to provide themselves with it without delay, and study its pages diligently and deliberately." — The Edin-
burgh Medical and Surgical Journal.

•'Judging from a single number only of this work, we have no hesitation in saying'that, if the remaining
portions correspond at all with the first, it will be by far the most complete and scientific System of Surgery
in the English language. We have, indeed, seen no work which so nearly comes up to our idea of what
such a procUiclion should be. both as a practical guide and as a work of reference, as this ; and the fact that
it has passed through six editions in Germany, and been translated into seven languages, is sufficiently.con-
vjncing proof of its value. It is methodical and concise, clear and accurate, omitting all minor details and
fruitless speculations, it gives us ail the information we want in the shortest and simplest form." — 2'Ae New
York Journal of Medicine.

'• Nor do these parts, in any degree, fall short of their predecessors, in the copiousness and value of their
details. The work certainly forms an almost unique curiosity in medical literature, in the fact that the
notes occupy a larger portion of the volume than the original matter, an arrangement which is constantly
appearing to render the text subsidiary to its illustrations. Still this singularity of manner does not at all
detract from the value of the matter thus disposed."— T^e London Medical Gazette.

'•This work has long been the chief text-book on Surgery in the principal schools of Germany, and the
publication of five editions of it in the original and of translations into no less than eight foreign languages,
shows the high estimation in which it is held. As a systematic work on Surgery it has merits of a high order.
It is methodical and concise— and on the whole clear and accurate. The most necessary information is
conveyed in the shortest and simplest form. Minor details and fruitless speculations are avoided. It is in
fact, essentially a practical book. This work was first published nearly twenty years ago, and its solid and
permanent reputation has no doubt led Mr. South to undertake the present translation of the latest edition
of it, which, we are informed, is still passing through the press in Germany. We should have felt at a loss
lo select any one better qualified for the task than the translator of Otto's Compendium of Human and Com-
parative Pathological Anatomy— a surgeon to a large hospital whose industry and opportunities have
enabled him to keep pace with the improvements of his time." — TAe Medico-Chirurgical Review.

" Although Great Britain can boast of some of the most skillful surgeons, both amongjier past and her present
professorsof that branch of medical scieiice.no work professing to be a complete system of Surgery has been
published in the British dominions since that of Benjamin Bell, now more than half a century old.

''This omission in English medical literature is fully and satisfactorily supplied by the translation of Profes-
scr Chelius's System of Surgery by agentleman excellently fitted for the task, both by his extensive reading,
and the opportunities of practical experience which he has enjoyed for years as surgeon to one of our largest
metropolitan hospitals. The fact of Professor Chelius's work having been translated into seven languages is
wifficienl proof of the estimation in which it is held by our continental brethren, and the Engli.sh Edition,
now in course of publication, loses none of the value of the original from the treatment received at the hands
of its translator. The notes and additions of Professor South are numerous, and contain the opinions result-
ing from his vast experience, and from that of his colleague." — The Medical Times.

"It ably maintains the character formerly given, of being the most learned and complete systematic
treatise now extant The descriptions of surgical diseases, and indeed the whole of the pathological depart-
raent, are most valuable."— TAe Edinburgh Medical and Siirgical Journal.

Ojr Persons wishing this work sent to them by mail, in parts, can remit Ten Dollars, for
'Which a -»et will be sent by the publishers, free of postage, together with a copy of "The
j^edical Jilews and Library" for one year.

LEA & BLANCHAED'S PUBLICATIONS.

GHEUUS'S SURGERY, CONTINUED.

The publishers annex a very condensed summary orthe contents of Chelius's Surgery, showing
the complete and systematic manner in which the whole subject is divided and treated.

I. Division. — Of Inflammation.

1. Qf inflammation in general.

2. Qf some peculiar kinds of inflammation.

a. Of erysipelas ; 6. Of burns ; c. Of frost-
bite ; d. Of boils ; e. Of carbuncle.

3. Qf inflammation in some special organs.

a. Of inflammation of the tonsils ; b. Of the
parotid gland ; c. Of the breasts ; d. Of
the urethra ; e. Of the testicle ; /. Of the
muscles of the loins; g. Of the nail
joints ; h. Of the joints, viz.

a. Of the synovial membrane ; b. Of the car-
tilages ; c. Of the joint-ends of the bones,
viz., aa. in the hip-joint; 66. in the
shoulder-joint ; cc. in the knee-joint ;
and so on.
II. Division. — Diseases which consist in a dis-
turbance of physical connexion.

I. Fresh solutions of continuity.

A. Wounds ; B. Fractures.

II. Old solutions,

A. Which do not suppurate, viz.

a. False joints ; 6. Hare-lip ; c. Cleft in
the soft palate ; d. Old rupture of
the female perineum.

B. Which do suppurate, viz.
i. Ulcers.

1. In general.

2. In particular.

a. Atonic ; 6. Scorbutic ; c. Scrofulous ;
d. Gouty ; e. Impetiginous ; /. Vene-
real ; g. Bony ulcers or caries.
ii. Fistulas.

a. Salivary fistula ; 6. Biliary fistula ; c. Faecal
fistula and artificial anus ; d. Anal fistula ;
e. Urinary fistula.

III. Solutions of continuity by changed position of

parts.
1. Dislocations; 2. Ruptures; 3. Prolapses;
4. Distortions.

IV. Solutions of continuity by unnatural distention.

1. In the arteries, aneurisms ; 2. In the veins,
varices ; 3. In the capillary-vascular sys-
tem, teleangiectasis.

III. Division. — Diseases dependent on the unna-
tural adhesion of parts.

1. Anchylosis of the joint-ends of bones ; 2. Grow-
ing together and narrowing of the aperture
of the nostrils ; 3. Unnatural adhesion of the
tongue ; 4. Adhesion of the gums to the
cheeks; 5. Narrowing of the oesophagus ; 6.
Closing and narrowing of the rectum ; 7.
Growing together and narrowing of the pre-
puce ; 8. Narrowing and closing of the ure-
thra ; 9. Closing and narrowing of the vagina
and of the mouth of the womb.

IV. Division. — Foreign bodies.

1 . Foreign bodies introduced externally into our

organism.
a. Into the nose ; 6. Into the mouth ; c. Into
the gullet and intestinal canal ; d. Into
the wind-pipe.

2. Foreign bodies formed in our organism by the

retention of natural products.

A. Retentions in their proper cavities and

receptacles.

a. Ranula ; 6. Retention of urine ; c.
Retention of the foetus in the womb
or in the cavity of the belly, (Caesa-
rean operation, section of the pubic
symphysis, section of the belly.)

B. Extravasation external to the proper cavi-

ties or receptacles.

a. Blood swellings on the heads of new-
born children; 6. Haematocele; c.
Collections of blood in joints.

3. Foreign bodies resulting from the accumulation

of unnatural secreted fluids,
a. Lymphatic swellings ; 6. Dropsy of joints ;
c. Dropsy of the bursae mucosae ; d. Wa-
ter in the head, spina bifida; e. Water
in the chest and empyema; /. Dropsy
of the pericardium ; g. Dropsy of the
belly ; h. Dropsy of the ovary ; i. Hy-
drocele.

4. Foreign bodies produced from the concretion of

secreted fluids.

V. Division. — Diseases which consist in the de-
generation of organic parts, or in the produc-
tion of new structures.

1. Enlargement of the tongue ; 2. Bronchocele ;
3. Enlarged clitoris; 4. Warts; 5. Bunions;
6. Horny growths; 7. Bony growths ; 8. Fun-
gus of the dura mater; 9. Fatty swellings ;
10. Encysted swellings; 11. Cartilaginous
bodies in joints; 12. Sarcoma; 13. Medul-
lary fungus ; 14. Polypus ; 15. Cancer.

VI. Division. — Loss of organic parts.

1. Organic replacement of already lost parts, es-

pecially of the face, according to the Taglia-
cotian and Indian methods.

2. Mechanical replacement : Application of arti-

ficial limbs, and so on.

VII. Division. — Superfluity of organic parts.

VIII. Division. — Display of the elementary ma*
nagement of surgical operations.

General surgical operations : Bleeding, cupping,
application of issues, introduction of setons,
amputations, resections, and so on.

DRUITT'S SURGERY. New Edition-Wow Ready, 1847.

THE PRINCIPLES AND PRACTICE OF MODERN SURGERY..

By ROBERT DRUITT, Surgeon.

THIRD AMERICAN FROM THE THIRD LONDON EDITION
Illustrated with one hundred and fifty-three wood engravings.
WITH NOTES AND COMMENTS,
BY JOSHUA B. FLINT, M.D, M. M., S. S., &c. &c.
In One very neat Octavo Volume of about Five Hundred and Fifty Pages.
In presenting this work to the American profession for the third time, but little need be said to TwITcit foir
it a continuation of the favor with which it has been received. The merits which have procured it this
favor, its clearness, concisenesSj and its excellent arrangement, will continue to render it the favorite text-
book of the student who wishes in a moderate space a compend of the principles and practice of S«rgery.

"This work merits our warmest commendations, and we strongly recommexjd it to young surgcu>iL9 M OT
admirable digest of the principles and practice of modern Surgery."— Merficai GazeUi. ■ - . - •»

LEA & BLANCHARD'S PUBLICATIONS.

SJOVT READir.

EOYLE'S MATERIA MEDICA.

MATERIA MEDICA AND THERAPEUTICS;

INCLUDINa THE PREPARATIONS OF THE PHARMACOPCEIAS OF LONDON,
EDINBURGH, DUBLIN, AND OF THE UNITED STATES.

WITH MANY NEW MEDICINES.

BY J. FORBES ROYLE, M.D, F. R. S.,

Late of the Medical Staff in the Bengal Army, Professor of Materia Medica and Therapeutics, King's Col-
lege, London, &c. &c.

EDITED BY JOSEPH CARSON, M.D.,

Professor of Materia Medica in the Philadelphia College of Pharmacy, fcc. &c.

WITH NINETY-EIGHT ILLUSTRATIONS.

l][j' See Specimen of the Cut»f but not of the Paper or Working^ on next Page*

In one large octavo volume of about 700 pages.

Being one of the most beautiful Medical works published in this Country.

The want has been felt and expressed for some time, of a text-book on Materia Medica, which
should occupy a place between the encyclopaedic works, such as Pereira, and the smaller treatises
which present but a meagre outline of the science. It has been the aim of the author of the
present work to fill this vacancy, and by the use of method and condensation, he has been enabled
to present a volume to the student, which will be found to contain what is necessary in a complete
and thorough text-book of the science, encumbered with few unnecessary details. The editor.
Dr. Carson, has added whatever was wanted to adapt it to the Pharmacopoeia of the United States,
and it is confidently recommended to the student and practitioner of medicine, as one of the best
text-books on the subject, now before the profession. — Great care has been taken in its mechanical
execution.

" Dr. Royle's manual, while it has the convenience of being in a portable form, contains as much
matter as would fill two octavo volumes in large type. Our readers will judge, from the remarks
which we have already made, that we think highly of this work. The subject is well treated, the
matter practical and well arranged, and we do not hesitate to recommend it as a most useful
volume to the student and practitioner. It is a good specimen of typography, and the engravings
are well executed." — Medical Gazette.

In regard to the yet more essential constituent, the literary portion of the work, no one who is
acquainted with the former productions of Dr. Royle, will doubt that the author has discharged his
duties with the same skill as the artist. The work is, indeed, a most valuable one, and will fill up
an important gap that existed between Dr. Pereira's most learned and complete system of materia
medica, and the class of productions at the other extreme, which are necessarily imperfect from
tlieir small extent. Such a work as this does not admit of analysis and scarcely of detailed critical
examination. It would, however, be injustice to the learned author not to state that, in addition
to what former works on the subject necessarily contained, the reader will find here not a little
that is either original, or introduced for the first time, more especially in the details of botany and
natural history, and in what may be termed the archaeology of drugs. — The British and Foreign
Medical Review.

Of the various works that have from time to time appeared on materia medica on the plan of the
one before us, there is none more deserving of commendation. From the examination which we
have given, accuracy and perspicuity seem to characterize it throughout, as a text book of refer-
ence to the student of medicine, and especially of pharmacy in its application to medicine, none
could be better.

We think that every one who can afford it should possess this excellent work, the value of which
has been greatly enhanced by the additions of Dr. Carson, than whom no one is more competent
to estimate it correctly, and to make such additions as may adapt it for American service. — The
Medical Examiner.

We have sufficiently extended our notice of the manual of materia medica and therapeutics, to
show that it possesses great merit, which will be a pretty sure guarantee of its acceptableness to
the profession. The department of materia medica is now so extended, that the treatises recently
issued from the press, partake of the nature of cyclopaedias. To the student, whether of pharmacy
solely or medicine, an extended manual as the present cannot but be regarded with favor. — The
. American Journal of Pharmacy.

We cannot, however, conclude without expressing our warm approbation of the volume as a
whole. It will certainly not detract from the author's high reputation. — The Medico-Chirurgical
Review,

Uj.

1 ■ ■, , »

SPECIMEN OF CUTS IN

RO YLE'S

MATERIA MEMCA AND THERAPEUTICS

aAfl:mT."n!/

^m

^u

10 LEA & BLANCHARD'S PUBLICATIONS.

" CHURCHILL'S MIDWIFERY.

ON THE THEORY AND PRACTICE OF MIDWIFERY.

BY FLEETWOOD CHURCHILL, M. D., M. R. I. A.,

Licentiate of the College of Physicians in Ireland ; Physician to the Western Lying-in-Hospual ; Lecturer on
Midwifery, &c., in the Richmond Hospital Medical School, &c. &.C.
WITH NOTES AND ADDITIONS,
BY ROBERT HUSTON, M.D.,
Professor of Materia Medica and General Therapeutics, and formerly of Obstetrics and the Disease of Wo-
men and Children in the Jefferson Medical College of Philadelphia; President of the Philadelphia
Medical Society, &c. &c.
SECOND AMERICAN EDITION.
WITH ONE HUNDRED AND TWENTY-EIGHT irtUSTRATIONS,
Engraved by Gilbert from Drawings by Bags and others.
In one beautiful octavo volume.
In this age of books, when much is written in every department of the science of medicine, it is a matter of
no small moment to the student, winch of the many he shall choose for his study in pupilage, and guide in
practice. In no department is the choice more difficult than in that of midwifery ; many excellent and truly
valuable treatises in thisdepartment of medicine have, within a few years past, been written; of this character
are ihose of Dewees, Velpeau. Meigs and R'gi)y, with due refpect to the auihorsoftlie works just cited, we are
compelled to admit, thai to Mr. Churchill has been reserved the honorof presenting to the profession one more
particularly adapted to ihe want and use of students, a work rich in statistics— clear in practice— and free in
siyle— possessing no small claims to our confidence. — The New York Journal of Medicine.

WILLIAMS' PATHOLOGY.

PRINCIPLES OF ME DICINE,

COMPttlSINO

6ENEBAL PATHOLOGY AND THERAPEUTICS,

XVl) A GBNEUAL VIEW OF

ETIOLOGY, NOSOLOGY, SEMEIOLOGY, DIAGNOSIS AND PROGNOSIS.
BY CHARLES J. B. WILLIAMS, M.D., F.R.S.,

FeliOw of the Royal College of Physicians, &c.

WITH NOTK8 AND ADHITIONS,

BY MEREDITH CLYMER, M. D., &c.

In one volume, octavo.

PEREIRA'S MATERIA MEDICA.

Willi nearly Three Hundred Engravings on Wood.

A NEW EDITION, LATELY PUBLISHED.

THE ELEMENTS OF

MATERIA MEDICA AND THERAPEUTICS.

co^iphehknuing

THE NATURAL HISTORY, PREPARATION, PROPERTIES, COMPO-
SITION, EFFECTS AND USES OF MEDICINES.
BY JONATHAN PEREIRA, M.D., F.R.S. and L.S.

Member of the Society of Pharmacy of Paris; Examiner in Materia Medica and Pharmacy of the University
of London; Lecturer on Materia Medica at the London Hospital. &c Sec.
Second American, from the last London Edition, enlarged afid improved.

WITH NOTES AND ADDITIONS BY JOSEPH CARSON, M.D.

In two volumes; octavo, containing Fifteen Hundred very large pages, illustrated by Two Hundred and

i?eventy-five Wood-cuts

This encycloprcdia of materia medica, for such it may justly be entitled, gives the fullest and most ample ex-
position of materia medica and its associate branches of any work hitherto published in ihe English language.
It abounds in research and erudition: its statements of facts are clear and meiliodically arranged, while its
therapeutical explanations are philosophical, and in accordance with sound clin:cal experience. It is equally
adapted as a text-iiook for students, or a work of reference for the advanced practitioner, and no one can
consult its pages without profit. The editor has performed his task with much ability and judgment. In the
first American edition, he adopted the PharmaeoptEia of the United Stales, and the formulaj .set forth in that
friandard authority; in the present he has introduced an account of substances that have recently attracted at-
tention by their therapeutic employment, together with the mode of forming the characters and uses of new
pharmaceutic preparations, and the details of more elaborate and particular chemical investigations, w^ith
respect to the nature of previously known and already described elementary principles— all the important
indigenous medicines of the United States heretofore known are also described. The work, however, is too
well known to need any further remark. We have no doubt it will have a circulation commensurate with its
extraordinary merits.— The New York Journal of Medicine.

•' An Encyclopedia of knowledge in that department of medical science— by the common consentofthe pro-
fession the most elaborate and scientific Treatise on Materia Medica in our language."— Wesiern Journal of
Medicine and Surgery.

LEA & BLANCHARD'S PUBLICATIONS. 11

WILSON'S ANATOMY. New Edition— Now Ready, 1847.

A SYSTEM OF HUMAN ANATOMY,
GENERAL AND SPECIAL.

BY ERASMUS WILSON, M,D.,

Lecturer on Anatomy, London.
THIRD AMERICAN FROM THE LAST LONDON EDITION.

EDITED BY P. B. GODDARD, A.M., M.D.,

Pfofesfor of Anatomy in the Franklin Medical Coljf-ge of Philadelpliia.

WITH TWO HUNDRED AND THIRTY-FIVE ILLUSTRATIONS BY GILBERT.

In one beautiful octavo volume of over SIX HUJWJDREH Iiarge jPag-ea,

Strongly Bound and sold at a low price.

Since the publication of the second American edition of this work, the author has issued a new
edition in London, in which he has carefully brought up his work to a level with the most advanced
science of the day. All the elementary chapters have been re-written, and such alterations made
through the body of the work, by the introduction of all new facts of interest, illustrated by appro-
priate engravings, as much increase its value. The present edition is a careful and exact reprint
of the English volume, with the addition of such other illustrations as were deemed necessary to a
more complete elucidation of the text; and the insertion of such of the notes appended to the last
American edition as had not been adopted by the author and embodied in his text; together with
such additional information as appeared calculated to enhance the value of the work. It may also
be stated that the utmost care has been taken in the revision of the letter-press, and in obtaining
clear and distinct impressions of the accompanying cuts.

It will thus be seen, that every effort has been used to render this text-book worthy of a con-
tinuance of the great favor with which it has been everywhere received. Professors desirous of
adopting it for their classes may rely on being always able to procure editions brought up to the
day.

This book is well known for the beauty and accuracy of its mechanical execution. The present
edition is an improvement over the last, both in the number and clearness of its embellishments;
it is bound in the best manner in strong sheep, and is sold at a price which renders it accessible
to all.

CONDIE ON CHILDREN.— New Edition, 1847.

A practicaiTtreatise on

THE DISEASES OF CHILDREN,

BY D. FRANCIS CONDIE, M. D,

Fellow of ihe College of Physicians, Member of the American Philosophical Society, &c.
In one large octavo volume.

iHr" The publishers would particularly call the attention of the profession to an examination of this book.

In the preparation of a new edition of the present treatise, every part of the work has been subjected to a
careful revision; several portions have been entirely rewritten; wMiile, throughout, numerous additions
have been made, comprising all the more important facts, in reference to the nature, diagnosis, and treat-
ment of the diseases of infancy and childhood, ihat have been developed since the appearance of the first
edition. It is wiih some confidence that the author presents this edition as embracing a full and connected
view of the actual state of the pathology and therapeutics of those aifections which most usually occur be-
tween birth and puberty.

This work is being introduced, as a text-book, very extensively throughout the Union.

CHURCHILL ON FEMALES. New Edition, 1847.— Now Ready.

THE DISEASEToF FEMALES,

INCLUDING THOSE OF '

PREGNANCY AND CHILDBED.

BY FLEETWOOD CHURCHILL, M D.,

Author of "Theory and Practice of Midwifery," &c. &c.
. FOURTH AMERICAN, FROM THE SECOND LONDON EDITION, WITH ILLUSTRATIONS.

EDITED, WITH NOTES,
BY ROBERT M. HUSTON, M.D.,&c.&c.

In one volume, 8vo.
The rapid sale of three editions of this valuable work, stamp it so emphatically with the approbation of the
profession of this country, that the publishers in presenting a fourth deem it merely necessary to observe,
that every care has been taken, by the editor, to supply any deficiencies which may have existed in former
impressions, and to bring the work fully up to the date of publication.

12 LEA & BLANCHARD'S PUBLICATIONS.

LIBRARY OF OPHTHALMIC MEDICINE AND SURGERY.
Brought up to 1847.

A TREATISE ON THE^^ISEASES OF THE EYE.

BY W. LAWRENCE, F.R.S.,

Surgeon Extraordinary to the Queen, Surgeon to St. Bartholomew's Hospital, &c. &c.
A NEW EDITION,

With many Modifications and Additions, and the Introduction of nearly two hundred Illustrations.

BY ISAAC HAYS, M. D.,

Surgeon to Wills' Hospital, Physician to the Philadelphia Orphan Asylum, &c. &c.

In one very large octavo volume of near 900 pages, with tw^elve plates and numerous wood-cuts through

the text.

This is among the largest and most complete works on this interesting and difficult branch of Medica
Science.

The early call for a new edition of this work, confirms the opinion expressed by the editor of its great
value, and has stimulated him to renewed exertions to increase its usefulness to practitioners, by incorporat-'
ing in it the recent improvements in Ophthalmic Practice. In availing himself, as he has freely done, of
the oi)servations and discoveries of his fellow-laborers in the same field, the editor has endeavored to do so
with entire fairness, always awarding to others what justly belongs to them. Among the additions which
have been made, may be noticed,— the descriptions of several afleclions not treated of in the original, — an
account of the catoptric examination of the eye, and of its employment as a means of diagnosis.— one hun-
dred and seventy-six illustrations, some of ihem from original drawings,— and a very full index. There have
also been introduced in ihe several chapters on the more important diseases, the results of the editor's ex-
perience in regard to their treatment, derived Oom more than a quarter of a century's devotion to the subject,
during all of which period he has been attached to some public institution for the treatment of diseases of the
eye.

" We think there are few medical works which could be so generally acceptable as this one will be to the
profession on this side of the Atlantic. The want of a scientific and comprehensive treatise on Diseases
of the Eye, has been much deplored. That want is now well supplied. The reputation of Mr. Lawrence
as an Oculist has been long since fully established; his great merit consists in the clearness of his style
and the very practical tenor of his work. The value of tlie present beautiful edition is greatly enhanced,
by the important additions made by the editor. Dr. Hays has, for nearly a quarter of a century, been con-
nected with public institutions for the treatment of Diseases of the Eye, and few men have made better im-
provement than he has. of such extensive opportunities of acquiring a thorough knowledge of the subject.
The wood-cuts are executed with great accuracy and beauty, and no man, wlio pretends to treat diseases
of the eye, should be without this work."— I-ancef.

JONES ON THE EYE. Now Ready.

THE PRINCIPLESAND PRACTICE
OF OPHTHALMIC MEDICINE AND SURGERY.

By T. WHARTON JONES, F.R.S., &c. &c.

-WITH ONE HUNDRED AND TEN ILIiUSTRATIONS.

EDITED BY ISAAC HAYS, M.D., &c.

In One very neat Volume, large royal 12mo., idth Four Plates, plain or colored, and Ninety-
eight well executed Wood-cuts.

This volume will be found to occupy a place hitherto unfilled in this department ofmedical science.
The aim of the author has been to produce a work which should, in a moderate compass, be suffi-
cient to serve both as a convenient text-book for students and as a book of reference for practitioners,
suitable for those who do not desire to possess the larger and encyclopaBdic treatises, such as
3-..awrence's. Thus, by great attention to conciseness of expression, a strict adherence to arrange-
ment, and the aid of numerous pictorial illustrations, he has been enabled to embody in it the prin-
ciples of ophthalmic medicine, and to point out their practical application more fully than has
Vjeen done in any other publication of the same size. The execution of the work will be found
to correspond with its merit. The illustrations have been engraved and printed with care, and the
whole is confidently presented as in every way worthy the attention of the profession.

" We are confident that the reader will find, on perusal, that the execution of the work amply fulfils the
promise of the preface, and sustains, in every point, the already high reputation of the author as an ophthal-
mic surgeon, as well as a physiologist and pathologist. The hook is evidently the result of much labor and
research, and has heen written with the greatest care and attention ; it possesses that best quality which a
general work, like a system, or manual, can show, viz :— the quality of having all the materials whenccso-
ever derived, sollioroughly wrought up. and digested in the author's mind, as to come forthwith the freshness
and impressiveness of an original production. We regret that we have received the book at so late a period
as precludes our giving more than a mere Tiotice of it, as although essentially and necessarily a compilation,
it caivtains many things which we should be glad to reproduce in our pages, whether in the shapt; of new
pathological views, of old errors correctt'd. or of sound principles of practice in doubtful cases clearly laid
down. But we dare say most of our readers will shortly have an opportunity of seeing these in their original
locality, as we entertain little doubt that this book will become what its author hoped it might become, a
manual for daily reference and consultation by the student and the general practitioner. The work is
marked by that correctness, clearness and precision of style which distinguish all the productions of the
learned ainhoT.''— The British a?id Foreign Medical Review.

LEA & BLANCHARD'S PUBLICATIONS. 13

NEW AND COMPLETE MEDICAL BOTANY.

NOW EEADY.

medicalIotany,

OR, A DESCRIPTION OF ALL THE MORE IMPORTANT PLANTS USED IN

MEDICINE, AND OF THEIR PROPERTIES, USES AND

MODES OF ADMINIS f-RATION.

BY R. EGLESFELD GRIFFITH, M.D., &c. &c.

In one large octavo volume.

With about three hundred and fifty Illustrations on Wood.
Specimens of the Cuts are annexed, but not so well printed as in the work, nor on as good paper.

This work is intended to supply a want long felt in this country, of some treatise present-
ing correct systematic descriptions of medicinal plants, accompanied by representations of
the most important of them, and furnished at a price so moderate as to render it generally
accessible and useful. In the arrangement, the author has treated more fully of those
plants which are known to be of the greatest importance; and more especially of such as
are of native origin ; while others, rarely used, are briefly noticed, or mentioned only by
name. In all cases, the technical descriptions are drawn up in accordance with the existing
.state of botanical knowledge, and in order that these maybe fully appreciated, even by those
not proficients in the science, an Introduction has been prepared, containing a concise view
of Vegetable Physiology, and the Anatomy and Chemistry of Plants. Besides this, a very
copious GLossAnx of botanical terms has been appended, together with a most complete
Index, giving not only the scientific but also the common names of the species noticed in
it. It will thus be ?^Qen. that the work presents a view not only of the properties and medical
virtues of the various species of the vegetable world, but also of their organization, compo-
sition and classification.

To the student, who is really anxious to study Botany for those great purposes which ren-
der it so necessary for the advancement of Medical Science, and who has been obliged to
rest satisfied with such imperfect knowledge as can be obtained from the different treatises
on the Materia Medica, the present work will be of great utility as a text-book and guide in
his researches, as it presents in a condensed form, all that is at present known respecting
those vegetable substances which are employed to alleviate suffering and to minister to the
wants of man. It will also be found extremely convenient to practitioners through the
country, who are anxious to obtain a knowledge of the medicinal plants occurring in their
vicinity, and who are unwilling to procure the scarce and high-priced works which are at
present the only ones accessible on this important branch of medical knowledge.

Great care has been taken to render the mechanical execution satisfactory.

NOW PREPARING,
AND TO BE READY BY AUGUST NEXT,

AN ANALYTICAL COMPEND OP THE YARIODS BRANCHES OP

PRACTICAL MEDICINE, SURGERY, ANATOMY,

MIDWIFERY, DISEASES OF WOMEN AND CHILDREN,
•Jflattria Jfledicu and Therapeutics^ Phifsiology^

By JOHN NEILL, M. D ,

Demonstrator of Anatomy in the University of Pennsylvania, and

F. GURNEY SMITH, M.D.,

Lecturer on Physiology in the Philadelphia Association for Medical Instruction.
To make one large royal Duodecimo volume, with numerous Illustrations on Wood.
It is the intention of the publishers to page this work in such a way, that it can be done up in
separate divisions, and in paper to go by mail; no one division will cost over 50 cents, thus pre-
senting separate MANUALS on the various branches of medicine, and at a very low price.

SPECIMEN OF THE ILlUSTRiTIONS IN

GRIFFITH'S MEDICAL BOTANY.

LEA & BLANCHARD'S PUBLICATIONS. 15

THE GREAT MEDICAL LIBRARY.
THE CYCLOP/EDIA OF PRACTICAL MEDICINE j

COMPRISING TREATISES ON THE

NATURE AND TREATMENT OF DISEASES, '

MATERIA MEDICA AND THERAPEUTICS,

DISEASES OF WOMEN AND CHILDREN,
MEDICAL JURISPRUDENCE, &c. &c.

EDITED BY

JOHN FORBES, M. D., F. R. S.,
ALEXANDER TWEEDIE, M.D., F.R.S.,

AXD

JOHN CONOLLY, M.D.

REVISED, WITH ADDITIONS,

By ROBLEY DUNGLISON, M. D.

THIS WORK IS NOW COMPLETE, AND FORMS

FOUR LARGE SUPER-ROYAL, OCTAVO VOLUMES.

CONTAINING THIRTY-TWO HUNDRED AND FIFTY-FOUR

UNUSUALLY LARGE PAGES IN DOUBLE COLUMNS,

PRINTED ON GOOD PAPER, WITH A NEW AND CLEAR TYPE.
THE WHOLE WELL AND STRONGLY BOUND,
WITH RAISED BANDS AND DOUBLE TITLES.
Or, to he had in twenty-four parts, at Fifty Cents each.

For a list of Articles and Authors, together with opinions of the press, see Supplement to the No-
vember number of the Medical News and Library for 1845.

This work having been completed and placed before the profession, has
been steadily advancing in favor with all classes of physicians. The nu-
merous advantages which it combines, beyond those of any other work ; the
weight which each article carries with it, as being the production of some
physician of acknowledged reputation who has devoted himself especially
to the subject confided to him; the great diversity of topics treated of; the
compendiousness with which everything of importance is digested into a
comparatively small space ; the manner in which it has been brought up
to the day, everything necessary to the American practitioner having been
added by Dr. Dunglison ; the neatness of its mechanical execution ; and
the extremely low price at which it is afforded, combine to render it one of
the most attractive works now before the profession. As a book for con-
stant and reliable reference, it presents advantages which are shared by no
other work of the kind. To country practitioners, especially, it is abso-
lutely invaluable, comprising in a moderate space, and trifling cost, the
matter for which they would have to accumulate libraries, w^hen removed
from public collections. The steady and increasing demand with w^hich
it has been favored since its completion, shows that its merits have been
appreciated, and that it is now universally considered as the

LIBRARY FOR CONSULTATION AND REFERENCE.

SMITH & HORNER'S ANATOMICAL ATLAS.

W

Just Published, Price Five Dollars in Parts.

AN

ANATOMICAL ATLAS
ILLUSTRATIVE OF THE STBUCTnilE OF THE HUMAN BOUT.

BY HENRY H. SxMITH, M. D.,

Feiloio of the College of Physicians^ ^c.
UiN'DER THE SUPERVISION OF

WILLIAM E. HORNER, M. D.,

Professor of Anatomy in t/ie University of Fetmsylvamcu ,

In One large Volume, Imperial Octavo.

This work is but just completed, having been delayed over the time intended by the great difficulty in giving
to the illustrations the desired finish and perfection. It consists of five pans, whose contents are as lbllovtr«:

Part I. The Bones and Ligaments, with one hundred and thirty engravings.

Part II. The Muscular and Dermoid Systems, with ninety-one engravings.

.Part III. The Organs of Digestion and Generation, with one hundred and ninety-one engravings.

Part IV. The Organs of Respiration and Circul-alion, with ninety-eight engravings.

Part V. The Nervous System and the Senses, with one hundred and twenty-six engravings.
Forming altogether a complete System of Anatomical Plates, of nearly

SIX HUNDRED AND FIFT^Y FIGURES,
executed in the best style of art, and making one iarge imperial octavo volume. Those who do not want it in
parts can have the work bound in extra cloth or sheep at an extra cost.

This work possesses novelty both in the design and the *"xecution. It is the first attempt to apply engraving
on wood, on a large scale, to the illustration of human anatomy, and the beauty of the parts issued induces the
publishers to flatter themselves with the hope of the perfect success of their undertaking. The plan of the
work is at once novel and convenient. Each page is perfect in itself, the references being immediately untler
the figures, so that llie eye takes in the whole at a glance, and obviates the necessity of continual reference
backwards and forwards. The cuts are selected from the best and most accurate sources ; and, where neces-
sary, original drawings have been made from the admirable Anatomical Collection of the University of Penu
gylvania. It embraces all the late beautiful discoveries arising from tlie use of the microscope in the investi-
gation of the minute structure of the tissues.

In the getting up of this very complete work, the publishers have spared neither pains nor expense, and tliey
now present it to the protession. with the full confidence that it will Ije deemed all that is wanted in a scientific
and artistical point of view, while, at the same time, its very low price places it within the reach of all.

It is particularly adapted to supply tlu place ofsktktons or subjects, cu the profession will see by examining the list
of plates

"These figures are well selected, and present a complete and accurate representationof that wonderful fabric,
the human body. The plan of this Atlas, which renders it so peculiarly conveniejit for the student, and its
superb artistical execuiioUj have been already pointed out. We must congratulate the student upon the
completion of this atlas, as it is the most convenient work of the kind that has yet appeared; and, we must
add, the very beautiful manner in which it is ' got up' is so creditable to the country us to be flattering to our
national pride." — American Medical Journal.

"This is an exquisite volume, and a beautiful specimen of art. "We have numerous Anatomical Atlases,
but we will venture to say that none equal it in cheapness, and none surjiass it in faithfulness and spirit. We
strongly recommend to our tnends. both urban and suburban, the purrlia.se of this excellent work, for which
both editor and publisher deserve tne thanks of the profession." — Mtdical Examiner.

"We would strongly reconnnend it, not only to the student, but also to the working practitioner, who,
although grown rusty in the toils of his harness still has the desire, and often the necessity, of refreshing his
knowledge in this fundamental part of the science of medicine." — New York Journal of Medicine and Surg,

" The plan of this Atlas is admirable, and its execution superior to any thing of the kind before published m
this country. Il is a real labour-saving affair, and we regard Us publication as the greatest boon that could be
conferred on the student of anatomy. It will be equally valuable to the practitioner, by alTording him an easy
means of recalling the details learned in tlie dissecting room, and wiiich are soon forgotten." — American Medi-
cal Journal.

" It is a beautiful as well as particularly useful design, which should be extensively patronized by physicians,
surgeons and medical siudtjnis." — Boston Med. and Surg. Journal.

" It has been the aim of the author of the Atlas to comprise in it tne valuable points of all previous works, to
embrace the latest microscopical observations on the anatomy of the tissues, and by placing it at a moderate
price to enable all to accjuire it who may need its assistance in the dissecting or operating room, or other field
of practice." — Wenern Journal of Med. and Surgery.

''These numbers complete the series of this beautiful work, which fully merits the praise bestowed upon the
earlier numbers. We regard all the engravings as possessing an accuracy only equalled by their beauty,
and cordially recommend tlie work to all engaged in tlie study of anatomy."— i\^K«> York Journal of Medicine
atul Surgery.

"A more elegant work than the one before us could not easily be placed by a physician upon tlie table of
his student.*' — Western Journal of Medicine and Surgery.

"We were much pleased with Part I, but the Second Part gratifies us still more, both as regards the attract-
ive nature of the subject. (The Dermoid and Muscular Systems.) and the beautiful artistical execution of the
.Ihistrations. We have here delineated the most accurate microscopic views of some of the tissues, as, for
instance, the cellular and adipose tissues, the epidermis, rete mucosum and cutis vera, the sebaceous and
perspiratory organs of the skin, the perspiratory giauds and hairs of the skm, and the hair and nails. Then
follows the general aiinloniy of the muscles, and. lastly, ilieir separate delineations. We would recommend
this Anatomical Atlas to our readers in the very strongest lernis." — New York Journal of Medicine and Sur-
gery.

LEA & BLANCHARD'S PUBLICATIONS. f?

HORNER'S ANATOMY;

NEW EDITION.

SPECIAL anatomy" AND HISTOLOGY.

BY WILLIAM E. HORNER, M.D.,

PROFESSOR OF ASATOMT IN THE UJflVEBSITI OF PENNSYLVANIA, &C., &C.

Seventh edition.

With many improvements and additions. In two octavo volumes, with illustrations on

wood.

This standard work has been so long before the profession, and has been so extensively-
used, that, in announcing? the new edition, it is only necessary to state, that it has under-
gone a most careful revision ; the author has introduced many illustrations relating to Mi-
croscopical Anatomy, and has added a large amount of text on those various points of
investigation that are rapidly advancing and attracting so much attention. This new edition
has been arranged to refer conveniently to the illustrations in Smith and Horner's Anato-
mical Atlas.

"The name of Professor Horner is a sufficient voucher for the fidelity and accuracy of
any work on anatomy, but if any further evidence could be required of the value of the pre-
sent publication, it is afforded by the fact of its having reached a seventh edition. It is
altogether unnecessary now to inquire into the particular merits of a work which has been
so long before the profession, and is so well known as the present one, but in announcing a
new edition, it is proper to state that it has undergone several modifications, and has been
much extended, so as to place it on a level with the existing advanced state of anatomy. —
The histological portion has been remodelled and rewritten since the last edition; numerous
wood cuts have been introduced, and specific references are made throughout the work to
the beautiful figures in the Anatomical Atlas, by Dr. H. H. Smith." — The American Medical,
Journal, for January, 1847.

HORNER' S^ISSECTOR.

THE UNITED STATES DISSECTOR,

BEING A NEW EDITION, WITH EXTENSIVE MODIFICATIONS,
AND ALMOST REWRITTEN, OF

'^UORJVER^S PR^ICTIC^E, JUVJlTO^Wir.-^^

IN ONE VERY NEAT VOLUME, ROYAL 12jio.

With many Illustrations on Wood. "* *

The numerous alterations and additions which this work has undergone, the improve-
ments which have been made in it, and the numerous wood-cuts which have been intro-
duced, render it almost a new work.

It is the standard work for the Students in the University of Pennsylvania.

Some such guide-book as the above is indispensable to the student in the dissecting room,
and this, prepared by one of the most accurate of our anatomists, may claim to combine as
many advantages as any other extant. It has been so favorably received that the publish-
ers have issued the fourth edition, which comes forth embellished by various- wood cuts. —
The copy for which we are indebted to the publishers, although received by us a fortnight
since, gives proof in its appearance that it has already seen service at the dissecting table,
where students have found it a valuable guide. — The Western Journal of Medicine and Sur-
gery.

HOPE ON THE HEART.

A TREATISE ON THE DISEASES

OF THE HEART AWD GREAT VESSELS,

AND ON THE AFFECTIONS WHICH MAY BE MISTAKEN FOR THEM,
Comprising the author's view of the Physiology of the Heart's Action and Sounds as demonstrated by his ex-
periments on tlie Motions and Sounds in 1830. and on ihe Sounds in 1834 — 5.
BY J. HOPE, M. D., F. R. S., &c. &c.
Second American from the third London edition. W^ith Notes and a Detail of Recent Experiments.
BY C. W. PENNOCK, M. D., &c.
In one octavo volume of nearly six hundred pages, writh lithographic plates.

18 LEA & BLANCHARD'S PUBLICATION?.

WORKS BY PROFESSOR W. P. DEWEES.

NEW EDITIONS.

DEWEES'S^IDWIFERY.

A COMPREHENSIVE SYSTEM OF MIDWIFERY.

CHIEFLY DESIGNED TO FACILITATE THE INQUIRIES OF THOSE WHO MAY BE PUR-
SUING THIS BRANCH OF STUDY.

ILLUSTRATED BY OCCASIONAL CASES AND MANY ENGRAVINGS.
Eleventh Edition, with the Author^s last Improvements and Corrections.

BY WILLIAM P. DEWEES, M.D.,

LATE PROFESSOR OF MIDWIFERY IN THE UNIVERSITY OF PENNSYLVANIA, ETC.
In one volume, octavo,
' That this work, notwithstanding the length of time it has been before the profession, and the numerous treat-
ises that have appeared since it was written, should have still maintained its ground, and passed to edition after
edition, is sufficient proof that in it the practical talt-nts of the author were fully placed before the profes-
sion. Of the book itself it would be superfluous to speak, having been so long and so favorably known through-
out the country as to have become identified with American Obstetrical Science.

DEWEES ON FEMALES.

A TREATISE ON THE ISEASES OF FEMALES.

BY WILLIAM P. DEWEES, M. D., &c.,

LATE PROFESSOR OF MIDWIFERY IN THE UNIVERSITY OF PENNSYLVANIA, ETC.

EIGHTH EDITION,
With the Author's last Improvements and Corrections.

In one octavo volume^ with plates.

D E WEES ON^lflLDR E N.

A TREATISE ON THE

PHYSICAL AND MEDICAL TREATMENT OF CHILDREN,

BY WILLIAM P. DEWEES, M.D.,

LATE PROFESSOR OF MIDWIFERY IN THE UNIVERSITY OF PENNSYLVANIA, ETC. ETC.

NINTH EDITION.

In one volume octavo.

This edition embodies the notes and additions prepared by Dr. Dewees before his death, and will be found
much improved.

The objects of this work are, 1st. to teach those who have the charge of children, either as parent or guardian,
the most approved methods of securing and improving their physical powers. This is attempted by pointing
out the duties which the parent or the guardian owes for this purpose, to this interesting but helpless class of
beings, and the manner by which their duties shall be fulfilled. And 2d. to render available a long experience
to those objects of our affection when they become diseased. In attempting this, the author has avoided as
much as possible, "technicality," and has given, if he does not flatter himself too much to each disease of
which he treats, its appropriate and designating characters, with a fidelity that will prevent any two being
confounded together, with the best mode of treating them, that either his own experience or that of others has
suggested.

Physicians cannot too strongly recommend the use of this book in all families.

ASHWELL ON THE DISEASES OF FEMALES.

A PRACTICAL TREATISE ON THE

DISEASES PECULIAR TO WOMEN.

ILLUSTRATED BY CASES
DERIVED FROM HSPOITAL AND PRIVATE PRACTICE.

By SAMUEL ASHWELL, M.D.,

Member of the Royal College of Physicians ; Obstetric Physician and Lecturer to Guy's Hospital, &c.

Edited by PAUL BECK GODDARD, M. D.

The whole complete in one large octavo volume.
" The most able, and certainly the most standard and practical work on female diseases that we
have yet seen." — Medico-Chirurgical Review.

LEA & BLANCHARD'S PUBLICATIONS. 19

WATSON'S PRACTICE OF PHYSIC.

NEW EDITION BY CONDIE.

LECTURES ON THE

PRINCIPLES AND PRACTICE OF PHYSIC.

DELIVERED AT KING'S COLLEGE, LONDON,

By THOMAS WATSON, M.D., &c. &c.
Second American, from the Second Lofidon Edition.

REVISED, WITH ADDITIONS,

BY D. FRANCIS CONDIE, M. D.,

Author of a work on the "Diseases of Children," &c.

In One Octavo Volume
Of nearly ELEVEN HUNDRED Large Pages, strongly bound with raised bands.

The rapid sale of the first edition of this work is an evidence of its merits, and of its general favor with the
American practitioner. To commend it still more stronstly to the profession, the publishers have gone ?o x
great expense in preparing this edition with larger type, finer paper, and stronger binding with raised band-?.
It is edited with reference particularly to American practice, by Dr. Condie; and with these numerous ;tii-
provemenls, the price is still kept so low as to be within the reach of all, and to render it among the cheapest
works offered^to the profession. It has been received with the utmost favor !)y the medical press, both o'" lii ■*
country and of England, a few of the notices of which, together with a letter from Professor Chapman, are
submitted.

Philadelphia, September Ttth, 1844.
Watson's Practice of Physic, in my opinion, is among the most comprehen-
sive works on the subject extant, replete with curious and important matter, and
written with great perspicuity and felicity of manner. As calculated to do much
good, I cordially recommend it to that portion of the profession in this country
who may be influenced by my judgment.

N. CHAPMAN, M.D.,

Professor of the Practice and Theory of Medicine in the University of Pennsylvania.

"We know of no work better calculated for being placed in the hands of the student, and for a text-book, and
as such we are sure it will be very extensively adopted. On every important point the author seems to have
posted up his knowledge to the day." — American MedicalJournal.

One of the most practically usetul books that ever was presented to the student — indeed a more admirable
summary of general and special pathology, and of the application of therapeutics to diseases, we are free to
say has not appeared for very many years. The lecturer proceeds through the whole classification of human
ills, a capile ad calcem. showing at every step an extensive knowledge of his subject, with the ability of commu-
nicating his precise ideas in a style remarkable for its clearness and simplicity." — N. Y. Journal of Medi-
cine and Surgery.

" We are free to state that a careful examination of this volume has satisfied us that it merits all the com-
mendation bestowed on it in this country and at home. It is a work adapted to the wants of young practi-
tioners, combining as it does, sound principles and substantial practice. It is not too much to say that it is a
representative of the actual slate of medicine as taught and practised by the most eminent physicians of the
present day, and as such we would advise everyone about embarking in the practice of physic to provide him-
self with a copy of iV^— Western Journal of Medicine and Surgery.

VdCEUS PATHOLOGICAL ANATOMY.

THE

PATHOLOGICAL ANATOMY OF THE HUMAN BODY.

By JULIUS VOGEL, M.D., &c.

TRANSLATED FROM THE GERMAN, WITH ADDITIONS,

By GEORGE E. DAY, M.D., &c.

KUustwteti t)» uplnavtis of ©ae ?QimtJre"li IJlafn anli ©oloreti Hnflrabfng.?.

In One neat Octavo Volume.

In our last number we gave a pretty full analysis of the original of this very valuable work, to which we
must refer the reader. We have only to add here our opinion that the translator has performed his task in an
excellent manner, and has enriched the work with many valuable additions.— TAe British and Foreign Medical
Review.

It is decidedly the best work on the subject of which it treats in the English language, and Dr. Day, whose
translation is well executed, has enhanced its value by a judicious selection of the most important figures from
the atlas, which are neatly engraved.— TAe London Medical Gazette.

m LE\ & BLANCHARD'S PUBLICATIONS.

A NEW EDITION OF THE GREAT

M E D I a A L_L E Z I O 0 IT .

A Dictionary of

MEDICAL SCIENCE,

CONTAINING A CONCISE ACCOUNT OF THE VARIOUS SUBJECTS AND TERMS; WITH THE
FRENCH AND OTHER SYNONVMES; NOTICES OF CLIMATES AND OF CELE-
BRATED MINERAL WATERS; FORMULAE FOR VARIOUS OFFICINAL
AND EMPIRICAL PREPARATIONS, &c.

BY HOBLEY DUNGLISON, M. D.,

PROFESSOR OF THE INSTITUTES OF MEDICINE, ETC. IN JEFFERSON MEDICAL COLLEGE, PHILADELPHIA.

Sixth edition, revised and greatly enlarged. In one royal octavo volume of over 800 very large pages,
double columns. Strongly bound in the best leather, raised bands.

"The most complete medical dictionary in the English language."— Wtstern Lancet.

" We think that -the author's anxious wish to render the work a satisfactory and desirable— if not indispen-
sable—Lexicon, in which the student may search without disappointment for every term that has been
legitimated in the nomenclature of the science,' has been fully accomplis-hed. Such a work is much needed
by all medical students and young physicians, and will doubtless continue in extensive demand. It is a
lasting monument of the industry and literary attainments of the author, who has long occupied the highest
rank among the medical teachers of America "—TAe New Orleans Medical and Svrgkal Journal

" The sinriple announcement of the fact that Dr. Dunglison's Dictionary has reached a sixth edition, is almost
as high praise as could be bestowed upon it by an elaborate notice. It is one of those standard works that have
been ' weighed in the balance and (not) been found wanting ' It has stood the test of experience, and the fre-
quent calls for new editions, prove conclusively that it is held by the profession and by students in the highest
estimation. The present edition is not a mere reprint of former ones; the author has for some time been
laboriously engaged in revising and making such alterations and additions as are required by the rapid pro-
gress of our science, and the introduction of new terms mto our vocabulary. In proof of this it is stated ' that
the present edition comprises nearly two thousand five hundred subjects and terms not contained in the last.
Many of these had been introduced into medical terminology in consequence of the progress of the science,
and others had escaped notice in previous revisions.' We think that the earnest wish of the author has been
accomplished ; and that he has succeeded in rendering the work 'a satisfactory and desirable— if not indis-
pensal)le— Lexicon, in which the student may search, without disappointment, for every term that has been
legitimated in the nomenclature of the science.' This desideratum he has been enabled to attempt in suc-
cessive editions, by reason of the work not being stereotyped ; and the present edition certainly offers stronger
claims to the attention of the practitioner and student, than any of its predecessors. The work is got i\p in
the usual good taste of the publishers, and we recommend it in full confidence to all who have not yet supplied
themselves with so indispensable an addition to their libraries "—TVi* New York Journal of Medicine.

A NEW EDITION OF DUNGLISON'S HDMAN PHYSIOLOGY.

HUMAN PHYSIOLOGY,

WITH THREE HUNDRED AND SEVENTY ILLUSTRATIONS.
BY ROBLEY DUNGLISON, M.D.,

PKOFESSOR OF THE INSTITUTES OF MEDICINE IN THE JEFFERSON MEDICAL COLLEGE, PHILADELPHIA, ETC., ETC.

Sixth edition, greatly improved. — In two large octavo volumes, containing nearly 1350 pages.
" It is but necessary for the Author to say, that all the cares that were bestowed on the preparation of the
fit'th edition have been extended to the sixth, and even to a greater amount. Nothing of importance thai has
been recorded since its publication, has, he believes, escaped his aitniiitioa. Upwards of seventy illustrations
have been added ; and many of the former cuts have been replaced by others. The work, he trusts, will be
found entirely on a level with the existing advanced state of physiological science."

In mechanical and artistical execution, this edition is far in advance of any former one.
The illustrations have been subjected to a thorough revision, many have been rejected and
their places supplied wilh superior ones, while numerous new wood-cuts have been added
■wherever perspicuity or novelty seemed to require them.

, "Those who have been accustomed to consult the former editions of this work, know with how much
care and accuracy every fact and opinion of weight, on the various subjects embraced in a treatise on
Physiology, are collected and arranged, so as to present the latest and best account of the science To such
■we need hardly say, that, in this respect, the present edition is not less distinguished than those which have
preceded it. In the two years and a half which have elapsed since the last or fifih edition appeared, nothing
of consequence that has been recorded seems to have been omitted. Upwards of seventy illustrations have
been added, and many of the former cuts have been replaced by others of better execution. These mostly
represent the minute structures as seen through the microscope, and are necessary for a proper comprehension
of the modern discoveries m this department " — The Medical Examiner.

The " Human Physiology" of Professor Dunglison has long since taken rank as one of the medical classics
in our language. Edition after edition has been issued, each more perfect than the last, till now we have the
sixth, with upwards of seventy new illustrations. To say that it is by far the best text-book of physiology ever
published in this country, is but echoing the general voice of the profession. It is simple and concise in style,
clear in illustration, and altogether on a level with the existing advanced state of physiological science. The
additions to the present edition are extremely numerous and valuable; scarcely a fact worth naming which
has a bearing upon the subject seems to have been omitted. All the recent writers on physiology, both in the
French, German and English languages, have been consulted and freely used, and the facts lately revealed
through the agency of organic chemistry and the microscope have received a due share of attention. As it is,
w^e cordially recommend the work as in the highest degree indispensable both to students and practitioners
of medicine. — New York Journal of Medicine.

The most full and complete system of physiology in our language.— ires/ern. Lancet.

LEA & BLANCHARD'S PUBLICATIONS. 21

DUNGLISON'S THERAPEUTICS.

NEW AND MUCH IMPROVED EDITION.

GENERAL THERAPEUTICS AND MATERIA MEDICA.

With One Hundred and Twenty Illustrations.

ADAPTED FOR A MEDICAL TEXT-BOOK.

BY ROBLEY DUNGLISON, M.D.,

Professor of Institutes of Medicine, &c. in Jeflerson Medical College; Late Professor of Materia Medica, &c.
in the Universities ot Virginia and Maryland, and in Jefferson Medical College.

Third Edition, Revised and Improved, in two octavo volumes, well hound.

In this edition much improvement will be found over the former ones The author has subjected it to a tho-
rough revision, and has endeavored to so modify the work as lo make it a more complete and exact exponent
of the present state of knowledge on the important subjects of which it treats. Thefavor with which the former
editions were received, demanded that the present should be rendered still more worthy of the patronage of the
profession, and this alteration will be found not only in the matter of the volumes, but also in the numerous
illustrations introduced and the general improvement in the appearance of the work.

•'This is a revised and improved edition of the author's celebrated book, entitled ' General Therapeutics;' an
account of the different articles of the Materia Medica having been incorporated with it. The work has, in
fact, been entirely remodelled, so that it is now the most complete and satisfactory exponent of the existingstate
of Therapeutical Science, within the moderate limits of a texi-book,of any hitherto published. What gives the
work a superior value, in our judgment, is the happy blendingof Therapeutics and Materia Medica as they are,
or ought lo be taught in all our medical schools; going no farther into the nature and lommercial history of
drugs, than is indisp^isable for the medical student. This gives to the treatise a clinical and practical charac-
ter, calculated to benefit in the highest degree, both students and practitioners. We shall adopt it as a text-
book for our classes, while pursuing this branch of medicine, and shall be happy to learn that it has been
adopted as such, in all of our medical institutions " — The N. Y. Journal of Metiicine.

•'Our junior brethren in America will find in these volumes of Professor Dunglison,a 'Thesaurus Medica-
MlNUMj'more valuable than a large purse of gold."— Z-owr^on Medico-Chiriirgical Review.

DUNGLISON ON NEW REMEDIES.

NEW EDITION, BROUGHT UP TO OCTOBER 1846.

NEW REMEDIES.

BY ROBLEY DUNGLISON, M.D., &c. &c.

Fifth edition, with extensive additions. In one neat octavo volume.

The numerous valuable therapeutical agents which have of late years been introduced into the Matera
Medica, render it a difficult matter for the practitioner to keep up with the advancement of the science, espe-
cially a.s the descriptions of them are difficult of access, being scattered so widely thiougli transactions of
learned societies, journals, monographs, &c. &c. To obviate this difficulty, and to place within reach of the
profession this important information in a compendious form, is the object of the present volume, and the num-
ber of editions through which it has passed show that its utility has not been underrated.

The author has taken particular care that this edition shall be completely brought up to the present day —
The therapeutical agents added, which may be regarded as newly introduced into the Materia Medica, to-
gether with old agents brought forward with novel applications, and which may therefore be esteemed as
'•New Remedies," are the following:— Benzoic Acid. t;hromic Acid, Gallic Acid. Nitric Acid, Phosphate of
Ammonia, Binelli Water, Brocchieri Water, Atropia Beerberia. Chloride of Carbon (Chloroform), Digitalia,
Electro-Magnetism. Ergotin, Oy-gall, Glycerin, llajmospasy. Hacmostasis, Hagcnia Abyssinica. Honey Bee,
Protochloride of Mercury and Quinia. Io<loform, Carbonate of liiihia, Sulphate of Manganese, Matico, DouMe
Iodide of Mercury and Morphia, lodhydrate of Morphia, Iodide of lodhydrate of Morphia, Muriate of Mor-
phia and Codeia, Naphthalin, Piscidia Erythritia, Chloride of Lead. Nitrate of Polassa, Arseniateof Quinia,
Iodide of Quinia, Iodide of Cinchonia. Iodide of lodhydrate of Quinia, Lactate of Quinia, Pyroacetic Acid,
(Naphtha, Acetone) Hyjiosulphate of Soda, Phosphate of Soda, Iodide of lodhydrate of fcirychnia, Double Iodide
of Zinc and Strychnia, Double Iodide of Zinc and Morphia, and Valerianate of Zinc.

( .''• A work like this is obviously not suitable for either critical or analytical review. It is, so far as it goes, a
dispensatory, in which an account is given of the chemical and physical properties of all the articles recenliy
added to the Materia Medicaand their preparations, with a noticeof the diseases for which they are prescribed,
the doses, mode of administration &c " — The Medical Examiner.

THE MEDIGAL STUDENT|

OR AIDS TO THE STUDY OF MEDICINE.

A REVISED AXD MODIFIED EDITION.

BY ROBLEY DUNGLISON, M. D.

In one neat 12mo. volume.

HUMAN HEALTH:

OR, THE INFLUENCE OF ATMOSPHERE AND LOCALITY. CHANGE OF AIR AND CLIMATE)

SEASONS, FOOD. CLOTHir^G, BATHIiVG AND MINERAL ^PRfNGS, EXERCISE,

SLEEP, CORPOREAL AND INTELLECTUAL PURSUITS. &c. &c.,

ON HEALTHY MAN: CONSTITUTING

ELEMENTS OF HYGIENE.

BY ROBLEY DUNGLISON, M. D.

A New Edition with many Modifications and Additions. In one Volume, 8vo.

«2 LEA & BLANCHARD'S PUBLICATIONS.

AMERICAN PRACTICE OF MEDICINE.

BY PROFESSOR DUNGLISON.

SECOND EDITION, MUCH IMPROVED. 'jlt^iji-

THE PRACTICE OF MEDICINE;

A TREATISE ON

SPECIAL PATHOLOGY AND THERAPEUTICS.

SECOND EDITION,

By ROBLEY DUNGLISON, M. D.

Professor of the Institutes of Medicine in the Jefferson Medical College; Lecturer on Clinical Medicine., S^'C

In Two large Octavo Volumes of over Thirteen Hundred Pages.

The Publishers annex a condensed statement of the Contents:
Diseases ef the Mouth, Tongue, Teeth, Gums, Velum Palati and Uvula, Pharynx and
(Esophagus, Stomach, Intestines, Peritoneum, Morbid Productions in the Peritoneum and
Intestines — Diseases of the Larynx and Trachea, Bronchia and Lungs, Pleura, Asphyxia,
Morbid Conditions of the Blood, Diseases of the Heart and Membranes, Arteries, Veins,
Intermediate or Capillary Vessels. — Spleen, Thyroid Gland, Thymus Gland and Supra
Renal Capsules, Mesenteric Glands.— Salivary Glands, Pancreas, Biliary Apparatus, Kidney,
Ureter, Urinary Bladder. — Diseases of the Skin, Exanthematous, Vesicular, Bullar, Pustular,
Papular, Squamous, Tuberculous, Maculae, Syphilides. — Organic Diseases of the Nervous
Centres, Neuroses, Nerves. — Diseases of the Eye, Ear, Nose. — Diseases of the Male and
Female Organs of Reproduction. — Fever. — Intermittent, Remittent, Continued, Eruptive,
Arthritic, Cachectic, Scrofulous, Scorbutic, Chlorotic, Rhachitic, Hydropic and Cancerous.

Notwithstanding the numerous and attractive works wliich have of late been issued on the Practice of
Physic, these volumes keep their place as a standard text-book for tlie student, and manual of reference for
the practitioner. The care with which the author embodies everythinsf of value from all sources, the industry
with which all discoveries of interest or importance are summed up in succeeding editions, the excellent
order and system which is everywhere manifested, and the clear and intelligible style in which his thoughts
are presented, render his works universal favorites with the profession.

'•In the volumes before us, Dr. Dunglison has proved that his acquaintance with the present facts and
doctrines, wheresoever originating, is most extensive and intimate, and the judgment, skill, and impartiality
with which the materials of the work have been collected, weighed, arranged, and exposed, are strikingly
manifested iii every chapter. Great care is everywhere taken to indicate the source of information, and
under the head of treatment, formulae of the most appropriate remedies are everywhere introduced. In con-
clusion, we congratulate the students and junior practitioners of America on possessing in the present
volumes a work of standard merit, to which they may confidently refer in» their doubts and dilllculties." —
Brit, and For. Med. Rev.

'' Since the foregoing observations were written, we have received a second edition of Dunglison's work,
a suiTicient indication of the high character it has already attained in America, and justly attained."— I6t<f.

"In the short space of two years, a second edition of Dr. Dunglison's Treatise on Special Pathology and
Therapeutics has been called for, and is now before the public in the neat and tasteful dress in which Lea
& Blanchard issue all their valuable publications. We do not notice the fact for the purpose of passing any
studied eulogy upon this work, which is now too well known to the profession to need the commendation of
the press. \

"A cursory examination will satisfy any one, that great labor has been bestowed upon these volumes,
and on a careful perusal it will be seen that they exhibit the present state of our knowledge relative to
special pathology and therapeutics. The work is justly a great favorite with students of medicine, whose
exigencies the learned author seems especially to have consulted in its preparation."— Western Jour, of
Med. and Surg.

'■ This is a work which must at once demand a respectful consideration from the profession, emanating as
It does from one of the most learned and indefatigable physicians of our country.

"This arrangement will recommend itself to the favorable consideration of all, for simplicity and com-
prehensiveness. We have no space to go into details, and, therefore, conclude by saying, that although
isolated defects might be pointed out, yet as a whole, we cheerfully recommend it to the profession, as
embracing much important matter which cannot easily be obtained from any other source."— Western Lancet.

Hasse's Pathological Anatomy.

AN ANATOMICAL DESCRIPTION OF THE DISEASES OF THE
ORGANS OP GXROULATIOir AlffD RESPIRATION.

BY CHARLES EWALD HASSE,
Professor of Pathology and Clinical Medicine in the University of Zurich., SfC.

Translated and edited by W, E. Swaine, M. D., &c.
lu one octavo volume. A new work, just ready— October, 1846.

LEA & BLANCHARD'S PUBLICATIONS. 23

BRODIE'S SURGICAL WORKS.

CLINICAL LECTUHES ON SUR6ERY|

DELIVERED AT ST. GEORGE'S HOSPITAL

By Sir BENJAMIN BRODIE, Bart., V. P. R. S.,

SERJEANT SURGEON TO THE QUEEN, ETC. ETC.

^ IN ONE NEAT OCTAVO VOLUME.

" It would not be easy to find in the same compass more useful matter than is embraced in each
of these discourses, or indeed in this volume. We the less regret the limited extracts we have it
in our power to make from it, because we feel sure that it will in a short time find its wiy into ali
the medical libraries in the country." — The Western Journal of Medicine and Surgery.

' LECTURES
ON THE DISEASES OF THE URINARY ORGANS.

SECOND AMERICAN FROM THE THIRD LONDON EDITION.

WITH ALTERATIONS AND ABBITIONS.

In One Small Octavo Volume^ Cloth.

This work has been entirely revised throughout, some of the author's views have been modified,
and a considerable proportion of new matter has been added, among which is a lecture on the
Operation of Lithotomy.

PATHOLOGICAL AND SURGICAL OBSERVATIONS
FROM THE FOURTH LONDON EDITION.

tDitI) tl)c ^uti)or's Alterations anb Ambitions.

In One Small Octavo Volume, Cloth.

"To both the practical physician and the student, then, this little volume will be one of much service, ina?-
much as we have here a condensed view of these complicated subjects thoroughly investigated by the aid of
the light affordeil hy modern Pathological Surgery."— JV. Y. Journal of Medicine.

^[Cr' These three works can be had bound together, forming a large volume of
BRODIE'S SURGICAL WORKS.

MILLER'S SURGICAL WORKS

THE PRINCIPLES OF SURGERY.

BY JAMES MILLER, F.R.S.E., F.R. C.S.E.,

Professor of Surgery in the University of Edinburg, &c.
In one neat octavo volume, to match the Author^s volume on " Practice.^^
" We feel no hesitation in expressing our opinion that it presents the philosophy of the science
more fully and clearly than any other work in the language with which we are acquainted." — Phi'
ladelphia Medical Examiner.

LATELY PUBLISHED.

THE PRACTICK OF SURGERY.

BY JAMES MILLER,

Professor of Surgery in the University of Edinburg.
In one neat octavo volume.
This work is printed and bound to match the " Principles of Surgery," by Professor Miller, lately
issued by L. & B. Either volume may be had separately.
" This work, with the preceding one, forms a complete text-book of surgery, and has been under-
taken by the author at the request of his pupils. Although as we are modestly informed in the
preface, it is not put forth in rivalry of the excellent works on practical surgery which already exist,
we think we may take upon ourselves to say ,that it will form a very successful and formidable
rival to most of them. While it does not offer the same attractive illustrations, with which some of
our recent text-books have been embellished, and while it will not, as indeed is not its design, set
aside the more complete and elaborate works of reference which the profession is in possession of,
we have no hesitation in stating that the two volumes form, together, a more complete text-book
of surgery than any one that has been heretofore offered to the student." — The Northern Journal
of Medicine.

LEA & BLANCHARD'S PUBLICATIONS.

CAB.P£:NT22B.'S INTSW "^OHK.

A MANUAL, OR ELEMENTS OF PHYSIOLOGY,

FOU THE USE OF THE MEDICAL STUDENT.

BY WILLIAM B. CARPEiNTER, M. D., F. R. S ,

FULLBRIAN PKOFESSOK OF PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN, ETC.

With one hundred and eighty illustrations. In one octavo volume of 5(56 pages. Elegantly printed to match
his " Principles of Human Physiology."

This work, though but a very short time published, has atlracled much attention from all engaged in teach-
ing the science of medicine, and has been adopted as a text-book l<y many schools throughout llie country. —
The clearness and conciseness with vvhich all the latest investigations are enunciated render it peculiarly
>veil suited for those commencing the study of medicine. It is proi'usely illustrated with beautiful wood en-
gravings, and is confidently presented as among the best elementary lexi-books on Physiology in the lan-
guage.

The merits of this work are of so high an order, and its arrangement and discussion of subjects so admi-
rably adapted to the wants of students, that we unhesitatingly connmend it io ther favorahle notice. This
work studied first, and thoi followed by the more elaborate treatise of Dunglison. or Muller, or others of similar
character, is decidedly the best course forthe student of physiology.— TAe Western Lancet.

CARPENTER'S HUMAN PHYSIOLOGY.

PRINCIPLES OF HUMAN PHYSIOLOGY,

WITH THEIR CHIEF APPLICAriONS TO

PATHOLOGY, HYGIENE, AND FORENSIC MEDICINE.

BY WILLIAM B. CARPENTER, M. D., F. R. S., &c.

Second American, from a New and Revised London Edition.

WITH NOTES AND ADDITIONS,

BY MEREDITH CLYMER, M. D., &c.

WUh Two Hundred and Sixteen Wood-cuts and other Illu»tratton»,

In one octavo volume, of about 650 closely and beautifully printed pages.

The very rapid sale of a large impression of the firtil edition is an evidence of the merits of this valuable
•work and that it has been duly appreciated by the profession of this country The publishers hope that the
present edition will be found still more worthy of approbation, not only from the additions of the author and
editor, but also from its superior execution, and the abundance of its illustrations. i\o less than eighty-five
wood-cuis and anotner lithographic plate will be found to have been added, affording the most material assist-
ance to the student.

'' We have much satisfaction in declaring our opinion that this work is the best systematic tr^^atise on pliy-
siology in our own language, and the best adapted for the student existing in any language."— iVIed/co-CAtrMrgt-
cal Review of London.

''The work as it now stands is the only Treatise on Physiology in the English language which exhibits a
clear and connt-cted, and comprehensive view of the present condition of that science."— JLo/xdon and Edin-
burgh Monthly Journal.

SUPPLEMENT TO THE ENCYCLOPJIDU AMERICANA, UP TO THE YEAR 1847.

ENCYCLOPiEDIA AMERICANA-Supplementary Vol.

A POPULAR DICTIONARY

OF ARTS, SCIENCES, LITERATURE, HISTORY, POLITICS AND

BIOGRAPHY.

VOL. XIV.

Edited by HENRY VETHAKE, LL.D.,

Vice-Provost and Professor of Mathematics in the University of Pennsylvania, Author of "A Treatise on Poli-
tical Economy."

In One large Octavo Volume of over Six Hundred and Fifty double columned pages.

The numerous subscribers who have been waiting the completion of this volume can now perfect
their sets, and all who want a Register of the Events of the last Fifteen Years, for the Whole
World, particularly embracing interesting scientific investigations and discoveries, can obtain this
volume separately, price Two Dollars uncut in cloth, or Two Dollars and Fifty Cents in leather,
to match the styles in which the publishers have been selling sets.

Subscribers in the large cities can be supplied on application at any of the principal bookstores ;
and persons residing in the country can have their sets matched by sending a volume in charge of
friends visiting the city.

Complete sets furnished at very low prices in various bindings.

'•The Conversations Lexicon (Encyclopfcdia Americana) has becoiue a household book in all the intelli-
gent families in America, and is undoubtedly the best depository of biographical, historical, geogrnphical and
political information of that kind which discriminating readers require. There is in the present volume much
matter purely scieutific, which was all the niore acceptable to us that it was unexpected."— <StWtOTa«'« Journal.

LEA & BLANCHARD'S PUBLICATIONS.

FOWNES' CHEMISTRY FOR STUDEJMTS.

elementary' CHEMISTRY.

THEORETICAL AND PRACTICAL. '

BY GEORGE FOWNES, Ph. D.,

Chemical Lecturer in the Middlesex Hospital Medical School, &c. &c.

With Numerous Illustrations. Edited, with Additions,
BY ROBERT BRIDGES, M. D.,

Professor ofGeneral and Pharmaceutical Chemistry in the Philadelphia College of Pharmacy, &c. &c.
In one large duodecimo volume, sheep or extra cloth.
Though this work has been so recently publislied, it has already been adopted as a text-book by many of ihe
Medical Institutions ihrougbotii the country. As a work for the first class student, and as an introduction to
the larger systems of Chemistry, such as Graham's, there has been but one opinion expressed concernijig u',
and It may )iow be considered hs

THE TEXT-BOOSL FOR THE CHEMICJiMj STUDEJTT.

" An admirable exposition of tlie present stale of chemical science, simply and clearly written, and display-
ing a thorough praetical knowledge of its details as well as a profound acquaintance with its principles. The
illustrations, and the whole getting-up of the book, merit our highest praise."— iJmis/t and Foreign Medical
Review.

•' Remarkable for its clearness, and the most concise and perspicuous work of the kind we have seen, admi-
ral.'ly calculated to prepare the student for the more e]ai)oraie treatises." — Pharmaceutical Journal.

This work of Fownes, while not enlarging on ihe subject as much as Graham, is far more lucid and expanded,
than the usual small introductory works. Persons using it may rely upon its being kept up to the day by fre-
quent revisions.

GRAHAM'S CHEMISTRY.

THE ELEMENTS~OF CHEMISTRY.

INCLUDING THE APPLICATION OF THE SCIENCE TO THE ARTS.
"With. Kumerous Illixstratlons.

Br THOMAS GRAHAM, F. R. S L. and E. D.,
Professor of Chemistry in University College, London, &c. &c.

WITH NOTES AND ADDITIONS,

Br ROBERT BRIDGES, M. D., &c. &c.
In one volume octavo.

SIMON'S CHEMISTRY OF MAN.

ANIMAL cllBMISTRir,

WITH REFERENCE TO THE PHYSIOLOGY AND PATHOLOGY OF MAN.
BY DR. J. FRANZ SIMON.

TRANSLATED AND EDITED BY

GEORGE E. DAY, M. A. & L. M. Cantab., &c.
With plates. In one octavo volume, of over seven hundred pages, sheep, or in tvjo parts, "boards.

This important work is now complete and may be had in one large octavo volume. Those who obtained the
first part can procure the second separate.

•'No treatise on physiological chemistry approaches, in fulness and accuracy of detail, the work which
stands at the head of this article. It is the production of a man of true German assiduity, who has added to his
own researches the results of the labors of nearly every other inquirer in this interesting branch of science —
The death of such a laborer, which is mentioned in the preface to the work as having occurred prematurely in
1342, is indeed a calamity to science. He had hardly reaehed the middle term of life, and yet had made himself
known all over Europe, and in our country, where his name has been familiar for several years as among the
most successful of the cultivators of the Chemistry of Man .... It is a vast repository of facts to which the
teacher and student may refer with equal satisfaction. "—J'/k Western Journal of Medicine and Surgery.

" The merits of the work are so universally known and acknowledged, as to need no further commendation
at our hands." — iV. Y. Journal of Medicine and Svrge/ry

THE CHEMISTRY OF THE FOIIR SEASONS— A NEW WORK.
THE CHEMISTRY OF THE FOUR SEASONS,

SPRING, SUMMER, AUTUMN AND WINTER.

AN ESSAY PRINCIPALLY CONCERNING NATURAL PHENOMENA ADMITTING OF

ILLUSTRATION BY CHEMICAL SCIENCE. AND ILLUSTRATING PASSAGES

OF SCRIPTURE.

BY THOMAS GRIFFITHS,

Professor of Chemistry in the Medical College of St. Bartholomew's Hospital, &c.
In One very neat Volume., royal 1 2mo., of Four Hundred and Fifty large Pages, extra cloth, illus-
trated with numerous Wood-cuts.
" VVe would especially recommend it to youths commencing the study of medicine, both as an incentive to
their natural curiosity and an imroduction to several of those branches of science which will necessarily soon
occupy their attention We would notice further, and with commendation, that a sound and rational natural
theology is spread through the whole work.^^— The British and Foreign Medical Revieto.

"This interesting and attractive volume is designed to illustrate by easy and familiar experiments, and in
popular language, many of the phenomena going on in the realm of nature through the ever-varying year, and
to exemplify and explain many beautiful scriptural allusions involving the play of chemical and philosophical
laws. Nor has the gifted author failed in accomplishing his laudable purpose. His agreeable style, the eor-
reciuess of his philosophical views, and especially ttxe high moral and religious bearing of his work, cannot
but secure for him the comnnendaiion and patronage of the intelligent and virtuous."— SowiAern Medical and
Sur gical Journal.

C5 . LEA & BLANCHARD'S PUBLICATIONS. -

LECTURES ON THE OPERATIONS OF SURGERY,

AND ON '

DISEASES AND ACCIDENTS REQUIRING OPERATIONS,

DELIVERED AT UNIVERSITY COLLEGE, LONDON.
BY ROBERT LTSTON, Esq., F. R. S., &c.

EBITEB, WITH NUMEROUS ALTEKATIONS AND ADDITIONS,

BY T. D. MUTTER, M.D.,

Professor of Surgery in the JefTerson Medical College, Philadelphia.

In One I^arge and Beautifully Printed Octavo Volume.

WITH TWO HUNDRED AND SIXTEEN ILLUSTRATIONS ON WOOD.

More than one-third of this volume is by Professor Miitter, embodying elaborate treatises on
Plastic Operations, Staphyloraphy, Club-Foot, Diseases of the Eye, Deformities from Burns, &c.&c.

iL SYSTEM OP PRAOTiaAL STTR^ERY.

BY WILLIAM FERGUSSON, F. R. S. E.

SECOND AMERICAN EDITION, REVISED AND IMPROVED.

With Tw^ Hundred and Fifty-two Illustrations from Drawings by Bagg, Engraved by Gilbert f

With Notes and Additional Illustrations,

BY GEORGE W. NORRIS,M. D., &c.

In one beautiful octavo volume of six hundred and forty large pages.

THE PRINCIPLES AND PRACTICE OF

OBSTETRIC MEDICINE AND SDRGERY,

IN REFERENCE TO TKE PROCESS OF PARTURITION.

ILLUSTRATED BT

Oi»« hundred and forty-eight Jjarg-e JPiffures on 55 JLithoffraphic JPlate$,

BY FRANCIS H. RAMSBOTHAM, M. D., &c.

A NEW EDITION, FROM THE ENLARGED AND REVISED LONDON EDITION.

In one large imperial octavo volume, well bound.

Philadelphia, August 6th, 1845.
Messrs. Lea & Bla.nchard.

Gentlemen :— I have looked over the proofs of Ramsbotham on Human Parturition, with its important im-
provements, from the new London edition.

This Work needs no commendation from me, receiving, as it does, the unanimous recommendation of the
British periodical press, as the standard work on Midwifery; "chaste in language, classical in composition,
happy in point of arrangement, and abounding in most interestmg illustrations."

To the American public, therefore, it is most valuable— from its mtrinsic undoubted excellence, and as being
the best authorized exponent of British Midwifery. Its circulation will, I trust, be extensive throughout our
country.

There is, however, a portion of Obstetric Science to which sufficient attention, it appears to me, has not been
paid. Through you, I have promised to the public a work on this subject, and although the continued occupa-
tion of my lime and thoughts in the duties of a teacher and practitioner have as yet prevented ihe fulfilment of
the promise, the day, I trust, is not distant, when, under the hope of being useful, I shall prepare an account of
the Mechanism of Labor, illustrated by suitable engravings, which may be regarded as an addendum to the
fitandard works of Ramsbotham, and our own Dewees.

Very respectfully, yours,

HUGH L. HODGE, M.D.,
Professor of Obstetrics, S(C. SfC, in. the Unuxrsity of Pennsylvania,

PROFESSOR CHAPMAN'S'!WORKS ON PRACTICE.

A COMPENDIUM OF LECTURES ON THE

THEORY AND PRACTICE OF MEDICINE.

DELIVERED BY PROFESSOR CHAPMAN IN THE UNIVERSITY OF PENNSYL-
VANIA. PREPARED, WITH PERMISSION, FROM DR CHAPMAN'S MA-
NUSCRIPTS, AND PUBLISHED WITH HIS APPROBATION,
By N. D. BKNKDICT, M. D. In one very neat octavo volume.

f^ This work contains the diseases not treated of in the two following.

LECTURE3 ON THE MORE IMPORTANT DISEASES OF THE

THORACIC AND ABDOMINAL VISCERA.

Delivered in the University of Pennsylvania, by N. Chapmabt, M. D., Professor of the Theory
and Practice of Medicine, &c. In one volume, octavo.

LECTURES ON THE MORE IMPORTANT

ERUPTIVE FEVERS, HEMORRHAGES AND DROPSIES,

AND ON GOUT AND RHEUMATISM,

Delivered in the University of Pennsylvania by N. Chapmax, M. D., Professor of the Theory
and Practice of Medicine, &c. &c. In one neat octavo volume.

LEA & BLANCHARD'S PUBLICATIONS. 27

A NEW MEDICAL DICTIONARY.

In one Volume, large 12mo., now ready, at a low price.

A DICTIONARY OF

THE TERMS USED IN MEDICINE

AND

THE COLLATERAL SCIENCES;
BY RICHARD D. HOBLYN, A. M., Oxon.

FIRST AMERICAN, FROM THE SECOND LONDON EDITION.

REVISED, WITH NUMEROUS ADDITIONS,

BY ISAAC HAYS, M D.,

Editor of the American Journal of the Medical Sciences.

A NEW AN^^COMPLEtFw^ ON FEVERS.

FEVERS;

THEIR DIAGNOSIS, PATHOLOGY AND TREATMENT.

PREPARED AND EDITED WITH LARGE ADDITIONS,

FROM THE ESSAYS ON FEVER IN

TWEEDIE'S LIBRARY OF PRACTICAL MEDICINE,
BY MEREDITH CLYMER, M. D.,

Professor of the Principles and Practice of Medicine in Franklin Medical College, Philadelphia /

Consulting Physician to the Philadelphia Hospital ; Fellow of the College of Physicians^ SfC. ^c.

In one octavo volume of 600 pa ges.

THE SURGICAL WORKS OF SIR ASTLEY COOPER.

THE ANATOMY AND SURGICAL TREATMENT OF

B^ SIK ASTLEY COOPER, BART.

Edited by C. ASTON KEY, Surgeon to Guy's Hospital, &c.
In one large imperial 8vo. volume, with over 130 Lithographic Figures.

ON THE STRUCTURE AND DISEASES OF THE TESTIS.

Illustrated by 120 Figures. From the Second London Edition.
BY BRANSBY B. COOPER, Esq.

AND ALSO ON THE AIN ATOMY OF THE THYMUS GLAND.

Illustrated hy fifty-seven Figures.
The two works together la one beautiful imperial octavo volume, illustrated with twenty-nine plates.

ANATOMY AND DISEASES OF THE BREAST, &c.

THIS LARGE AND BEAUTIFUL VOLUME CONTAINS THE ANATOMY OF THE BREAST
THE COMPARATIVE ANATOMY OF THE MAMMARY GLANDS; ILLUSTRA-
TIONS OF THE DISEASES OF THE BREAST ;

And Twenty-five Miscellaneous Surgical Papers, now first published in a collected form.

BY SIR ASTLEY COOPER, Bakt., F. R. S., &c.

The whole m one large imperial octavo volume, illustrated with two hundred and fifty-two figures.

A TREATISE ON DISLOCATIONS AND FRACTURES OF THE JOINTS.

By Sir ASTLEY COOPER, Bart., F. R. S., Sergeant Surgeon to the King, &c.

A New Edition much enlarged ;

Edited by BRANSBY COOPER, F. R. S., Surgeon to Guy's Hospital.

With additional observations from Professor JOHN C. WARREN, of Boston.

With numerous Engravings on Wood, after designs by Bagg, a Memoir and a splendid Portrait of Sir Astley

In one octavo volume.

LEA & BLANCHARD'S PUBLICATIONS.

OTHER WORKS

VARIOUS DEPARTIVIENTS

OF

MEDICINE AND SURGERY,

PUBLISHED

BY LEA <k BLANCH A RD.

AMERICAN JOURNAL OF THE MEDIC AlTscrENCES. Edited by Isaac Hays, M.D.
Published quarterly at $5 00 per annum.

ANDRAL ON THE BLOOD. Pathological Hi3Bmatology ; an Essay on the Blood in Dis-
ease. Translated by J. F. Meigs and Alfred Stille. In one octavo volume, cloth.

ARNOTT'S PHYSICS. The Elements of Physics in plain or non-technical language. A
New Edition. Edited by Isaac Hays, M. D. In 1 vol. 8vo., sheep, with 176 wood-cuts.

ABERCROMBIE ON THE STOMACH. Pathological and Practical Researches on Dis-
eases of the Stomach, Intestinal Canal, &c. Fourth Edition. In 1 vol. 8vo., sheep.

ABERCROMBIE ON THE BRAIN. Pathological and Practical Researches on the Dis-
eases of the Brain and Spinal Cord. A New Edition. In one octavo volume, sheep.

ALISON'S PATHOLOGY. Outlines of Pathology and Practice of Medicine. In three
parts, containing Preliminary Observations, Inflammatory and Febrile Diseases, and
Chronic or Non-Febrile Diseases. In one neat octavo volume, sheep.

BENNET'S PRACTICAL TREATISE ON INFLAMMATION, ULCER.ATION AND
INDURATION OF THE NECK OF THE UTERUS. In pne small 13mo. volume,
cloth.

BIRD ON URINARY DEPOSITS. Urinary Deposits, their Diagnosis, Pathology and The-
rapeutical Indications. In one neat octavo volume, cloth, with numerous wood-cuts.

BERZELIUS ON THE KIDNEYS AND URINE, in 1 vol. 8vo., cloth.

AUCKLAND'S GEOLOGY. Geology and Mineralogy, with reference to Natural Theology.
A Bridgewater Treatise. In two octavo volumes, wiih numerous maps, plates, &c.

BUDD ON DISEASES OF THE LIVER. In one octavo volume, sheep, with beautiful
colored plates and numerous woodcuts.

BRIDGEWATER TREATISES. The whole complete in 7 vols. Svo., containing Roget's
Animal and Vegetable Physiology, in 2 vols., with many cuts ; Kirby on the History,
Habits and Instinct of Animals, I vol. with plates ; Prout on Chemistry ; Chalmers on the
Moral Condition of Man ; Whewell on Astronomy ; Bell on the Hand ; Kidd on the Phy-
sical Condition of Man; and Buckland's Geology, 2 vols., with many plates and maps.

BARTLETT'S PHILOSOPHY OF MEDICINE. Essay on the Philosophy of Medical
Science. In two Parts. One neat octavo volume, extra cloth.

BRIGHAM ON MIND, &c. The Influence of Mental Excitement and Mental Cultivation
on Health. In one neat 12mo. volume, extra cloth.

BILLING'S PRINCIPLES OF MEDICINE. The First Principles of Medicine. From the
Fourth London Edition. In one octavo volume, cloth.

CARPENTER'S VEGETABLE PHYSIOLOGY. A Popular Treatise on Vegetable Phy-
siology. With numerous wood-cuts. In one I2mo. volume, extra cloth.

CLATER AND SKINNER'S FARRIER. Every Man his own Farrier. Containing the
Causes, Symptoms, and most approved Methods of Cure of the Diseases of Horses.
From the 28th London Edition. Edited by Skinner. In one 12mo. volume, cloth.

CLATER AND YOUATT'S CATTLE DOCTOR. Every Man his own Cattle Doctor.
Containing the Diseases of Oxen, Sheep, Swine, &c. Edited by Youatt, and revised by
Skinner. With Wood-cuts. In one volume, 12mo.

DURLACHER ON CORNS, BUNIONS, &c. A Treatise on Corns, Bunions, the Dis-
eases of Nails, and the General Management of the Feet. In one 12mo. volume, cloth.

ELLIOTSON'S MESMERIC CASES. In one octavo pamphlet.

ELLIS' FORMULARY. The Medical Formulary, being a collection of Prescriptions de-
rived from the Writings and Practice of the most eminent Physicians of America and
Europe. To which is added an Appendix, containing the usual Dietetic Preparations
and Antidotes for Poisons. By Benjamin Ellis, M. D. Eighth Edition, with extensive
Alterations and Additions. By Samuel George Morton, M, D. In one neat 8vo. volume.

ESQUIROL ON INSANITY. Mental Maladies, Considered in Relation to Medicine, Hy-
giene and Medical Jurisprudence. Translated by E. K. Hunt, M. D. &c. In I vol. Svo.

GUTHRIE ON THE BLADDER, &c. The Anatomy of the Bladder and Urethra, and
the Treatment of the Obstructions to which those passages are liable. In 1 vol. Svo.

HARRIS ON MAXILLARY SINUS. Dissertation on the Diseases of the Maxillary Sinus.
In one small octavo volume, cloth.

HARRISON ON THE NERVES. An Essay towards a correct Theory of the Nervous
System. In one octavo volume, sheep.

^UGHES ON THE LUNGS AND HEART. Clinical Introduction to the Practice of
Auscultation, and other Modes of Physical Diagnosis, intended to simplify the study of

LEA & BLANCHARD'S PUBLICATIONS. 29

the Diseases of the Heart and Lungs. By H. M. Hughes, M. D., &c. fn one 12mo.
volume, with a plate.

INTRODUCTION TO PRACTICAL ORGANIC CHEMISTRY; based on the Works of
Brande, Liebig and others. In 1 volunne, 18mo.. paper, price 25 cents.

INTRODUCTION TO VEGETABLE PHYSIOLOGY. With reference to the Works of
De Candolle, Lindley, &c. In 1 volume, 18mo., paper, price 25 cents.

KIRBY ON ANIMALS. The History, Habits and Instinct of Animals. A Bridgewater
Treatise. In one large volume, 8vo., with plates.

KIRBY AND SPENCE'S ENTOMOLOGY. An Introduction to Entomology ; or Elements
of the Natural History of Insects; comprising an Account of Noxious and Useful
Insects, of their Metamorphosis, Food, Stratagems, Habitations, Societies, Motions,
Noises, Hybernation, Instinct, &c, &c. In one large octavo volume, neat extra cloth,
with plates, plain or beautifully colored. From the sixth London Edition.

LAWRENCE ON RUPTURES. A Treatise on Ruptures, from the fifth London Edition.
In one octavo volume, sheep.

MAN'S POWER OVER HIMSELF TO PREVENT OR CONTROL INSANITY. One
vol. ISmo., paper, price 25 cents.

MAURY'S DENTAL SURGERY. A Treatise on the Dental Art, Founded on Actual Ex-
perience. Illustrated by 241 Lithographic Figures and 54 Wood-cuts. Translated by
J. B. Savier. In 1 octavo volume, sheep.

MULLER'S PHYSIOLOGY. Elements of Physiology. Translated by Wm. Bayly, M. D.,
and edited and arranged by John Bell, M. D. In one large octavo volume, sheep.

PRACTICAL ORGANIC CHEMISTRY. ISmo., sewed, price 25 cents.

PROUT ON THE STOMACH. On the Nature and Treatment of Stomach and Renal
Diseases. In I octavo volume, sheep, with colored Plates.

POPULAR MEDICINE, BY COATES. In one octavo volume, sheep, with Wood-cuts.

PHILIP ON INDIGESTION. A Treatise on Protracted Indigestion. In 1 vol., Svo.

PHILLIPS ON SCROFULA. Scrofula, its Nature, its Prevalence, its Causes, and the
Principles of its Treatment. In one neat octavo volume, cloth, with a Plate.

ROGET'S PHYSIOLOGY. A Treatise on Animal and Vegetable Physiology, with over
400 Illustrations on Wood. In two octavo volumes, cloth. A Bridgewater Treatise.

ROGET'S OUTLINES OF PHYSIOLOGY. Outlines of Physiology and Phrenology. la
one large octavo volume, cloth.

RIGBY'S MIDWIFERY. A System of Midwifery. With Wood-cuts. In I vol. Svo.

RICORD ON VENEREAL. A Practical Treatise on Venereal Diseases; with a Thera-
peutical Summary, and a Special Formulary. In 1 vol. 8vo., cloth.

ROBERTSON ON TEETH. A Practical Treatise on the Human Teeth, with Plates. One
small volume, octavo, cloth.

TAYLOR'S MEDICAL JURISPRUDENCE. With numerous Notes and Additions, and
References to American Practice and Law. By R. E. Griffith, M. D. In 1 vol., Svo.

THE CONNECTION BETWEEN PHYSIOLOGY AND INTELLECTUAL SCIENCE.
I vol. ISmo., paper, price 25 cents.

THOMPSON'S SICK ROOM, Domestic Management of the Sick Room, Necessary in Aid
of Medical Treatment for the cure of Diseases. Edited by R. E. Griffith, in one large
royal 12mo. volume, extra cloth, with Wood-cuts.

TRAILL'S MEDICAL JURISPRUDENCE. Outlines of a Course of Lectures on Medical
Jurisprudence. Revised, with numerous Notes. In one octavo volume, cloth.

TRIMNER'S GEOLOGY. A Text Book of Practical Geology and Mineralogy. With In-
structions for the Qualitative Analysis of Minerals. In one handsome octavo volume,
extra cloth, with 212 Wood-cuts.

WALSHE ON THE LUNGS. Physical Diagnosis of the Diseases of the Lungs. In one
neat l2mo. volume, extra cloth.

WILLIAMS AND CLYMER ON THE CHEST. A Treatise on the Diseases of the Re-
spiratory Organs, including the Larynx, Trachea, Lungs and Pleura. With numerous
Additions and Notes, by Meredith Clymer, M. D. In one neat Svo. volume, with cuts.

WILSON ON THE SKIN. A Practical and Theoretical Treatise on the Diagnosis,
Pathology and Treatment of Diseases of the Skin; arranged according to a Natural
System of Classification, and Preceded by an Outline of the Anatomy and Physiology
of the Skin. In one neat octavo volume, cloth.

WILSON'S DISSECTOR. THE DISSECTOR, OR PRACTICAL AND SURGICAL
ANATOMY. With 106 Illustrations. Modified and re-arranged by Paul B. Goddard,
M. D., &c. In one large royal 12mo. volume, sheep.

YOUATT ON THE HORSE. The Horse: containing a full account of the Diseases of
the Horse, with their Mode of Treatment; his Anatomy, and the usual Operations per-
formed on him ; his Breeding, Breaking and Management ; and Hints on his Soundness,
and Purchase and Sale. Together with a General History of the Horse ; a Dissertation
on the American Trotting Horse, how Trained and Jockeyed, an account of his remark-
able performances; and an Essay on the Ass and the Mule. By J. S. Skinner, Assist-
ant Postmaster-General, and Editor of the Turf Register. In one volume, octavo, with
numerous Cuts.

30 LEA & BLANCHARD'S PUBLICATIONS.

A TREATISE ON THE DISEASES OF FEMALES, ~

AND ON THE SPECIAL HYGIENE OF THEIR SEX.

WITH NUMEROUS WOOD-CUTS.

BY COLOMBAT DE L'ISERE,M.D.,

Chevalier of the Legion of Honor ; late Surgeon to the Hospital of the Rue de Valois, devoted to the

Diseases of Females, SfC. SfC.

TRANSLATED, WITH MANY NOTES AND ADDITIONS,

BY C. D. METGS, M. D.,

Frofessor of Obstetrics and Diseases of Women and Children in the Jefferson Medical College, ^c. ^e.

In one large volume, 8vo.

iroii.MTT ojy THE noa.

T H E ~D O G .

BY WILLIAM YOUATT.

WITH NUMEROUS AND BEAUTIFUL ILLUSTRATIONS.

EDIIED BY E. J. LEWIS, M. D., &c. &c.

tn One heaulifully printed Volume, Crown Octavo, with Twenty. four Plates, done up in richcrim-

son extra cloth.
" With this explanation of his connection with the work he leaves it, in the hope that it may
prove of value to the sportsman from its immediate relation to his stirring pursuits; to the general
reader from the large amount of curious information collected in its pages; and to the MEDICAL
STUDENT from the light it sheds on the PATHOLOGY AND DISEASES of the dog, by which he
will be surprised to learn how many ills that animal shares in common with the human race." —
Editor's Pkeface.

LANDRETH'S JOHNSON'S_GARDENERS' DICTIONARY.

JXT3T RBADT.

A DICTIONARY OF MODERN GARDENING.

BY GEORGE WILLIAM JOHNSON, Esa.,

Fellow of the Horticultural Society of India, &c. &c.

With One Hundred and Eighty Wood-Cuts.

EDITED, WITH NUMEROUS ADDITIONS,

BY DAVID LANDRETH, of Philabelphia.

Tn the American edition, many modifications and additions have been made, so as to render the work a com-
plete and satisfactory book of reference upon every subject connected with modern gardening in its most ex-
tended sense; while great care has been exercised in adapting it to the practice of every section of this country.

Numerous wood-cut illustrations have been added, and the publishers present a beautiful volume of near
650 pages, in a clear but small type, well done up in extra cloth, and at a very low price. Such a work has
long been needed by the many persons who cannot afford to purchase the large expensive work of Loudon.

Sold by all Booksellers, JYurserymen and Seedsmen in the United States,
CONTENTS OF THE

AMEBtCAN JOURNAL OF THE I^EDICAL SCIENCES,

For .Spril, 1847.

Memoirs and Cases — Art. I. History of seven cases of Pseudo-membranous Laryngitis, or True Croup.
By J. F. Meigs, M. D. II. Poisonous Properties of the Sulphate of Quinine. By Wm. O. Baldwin, M. D. III.
Removal of the Superior Maxilla for a tumour of the antrum; Apparent cure. Retuinof the disease. Second
operation. Sequel. By J. Marion Sims, M. D. [With a wood-cut] IV. Lacerationofthe Perineum. By John
V. Mettauer, M. D. V. Report of Cases treated in Cincinnati Commercial Hospital. By .lohn P. Harrison,
M. D. VI. Surgical Cases. By Geo. C. Blackman, M. D. [With a wood-cut.] VII. Cases of Paralysis
peculiar to the Insane. By Pliny Earle, M. D. VIH. Contributions to Pathology; being a Report of Fatal
Cases taken from the records of the U. S. Naval Hospital, New York. By W. S. W. Ruschenberger, M. D.
IX. Caseof Hydrops Pericardii suddenly formed, with Remarks. By S. Jackson, M. D. X. Case of Tuber-
cles in the pericardium, vena cava, columnse carnese, pleura, lungs, liver, &c., with Meningitis. By J. D.
Trask, M. D. XL On letting Blood from the Jugular in the Diseases of Children. By Charles C. Hildreth,
M.D.

Review. — XIT. Lectures on Subjects connected with Clinical Medicine ; comprising Diseases of the
Heart. By P. M. Latham, M. D.

Bibliographical Notices.— -XIII. Green on Diseases of the Air Passages. XIV. Condie on the Diseases of
Children. Second edition. XV. Royle's Materia Medica and Therapeutics. Edited by Carson. XVI. VogePs
Pathological Anatomy of the Human Body. Translated, with additions, by George E. Day. XVII. Trans-
actions of the College of Physicians of Philadelphia. From September to November, 1646, inclusive.
XVIII. Wharton Jones on the Principles and Practice of Ophthalmic Medicine and Surgery. Edited by
Isaac Hays, M. D. XIX. Wood on the Practice of Medicine. XX. Wernher's Manual of General and
Special Surgery. XXI. Baumgarten's Surgical Almanac for the years lc44 and 1845. XXII. Wilson's
System of Human Anatomy, General and Special. Third American from the third London edition. Edited
by Paul B Goddard, M. D. XXHI. Von Behr's Handbook of Human Anatomy, General, Special and
Topographical. Translated by John Birkelt.

LEA & BLANCH ARD'S PUBLICATIONS. 31

Contents of the Medical Journal Continued.

QUARTERLY RETROSPECT,

A SUMMARY OF THE IMPROVEMENTS AND DISCOVERIES IN THE MEDICAL SCIENCES.

Foreign Intelligence— Anatomy AND Physiology— 1. QMfA;e« on Intimate Structure of Bone. 2. Meckel
on Processor Secretion. 3. Blondlot on the Propertiesof the Bile. 4. .Bam?>rrg-§-e on Supplementary Spleen,
death from the patient being placed in the supine position. 5. Robinson on the Nature and Source of the
contents of the Foetal Stomach. 6. Prof. Bischoff on the Absorption of Narcotic Poisons by the Lymphatics.

Materia Medica and Pharmacy. — 7. Battley on Syrup of Iodide and Chloride of Iron. 8. Rlcord on Bro-
mide of Potassium as a substitute for the Iodide. 9. VoUlemier on Santonine. 10. GweftoMri on the changes
of composition which the Tincture of Iodine undergoes in keeping. 11. Mellon on the Action of the Acetate
of Morphia on Children.

Medical Pathology and Therapeutics and Practical Medicine. — 12. Bennett on Anormal Nutrition
and Diseases of the Blood. 13. Rostan on Acute Spinal Myelitis. 14. Rostan on Curability of Hypertrophy
of the Heart. 15. Crisp on Rupture of the left Ventricle of the Heart. 16. Francis on Aneurism of the Basi-
lar Artery. 17. Lombard^s Observations on Sudden deaths, probably dependent on Diseases of the Heart
and large Blood-vessels. 18. Carson on Obliteration of the Vena Cava Descendens. 19. Thompson on
Treatment of Chronic Bronchitis and Bronchial Asthma. 20. Muklbauerh Microscopic Researches on the
Absorption of Pus. 21. Briquet on Mercurial Ointment in Variola. 22. Bell on Rupture of Lateral Sinus of
Dura Mater. 23. Watts on Tubercles in Bones. 24. Gendrin on Hysterical Affections. 25. Cottereau's
Remedy for Toothache. 26. Prof Trousseau on Anatomy of Pneumonia in Infants. 27. Volz on Hooping
Cough an Exanthemata. 28. Crisp on Infantile Pleurisy. 29. Yowi on Abscess of the Brain in a Child. 30.
Trousseau on the Employment of Nux Vomica in the Treatment of St. Vitus' Dance.

Surgical Pathology and Therapeutics and Operative Surgery.— 3L Prof. Syme on Amputation at
the Shoulder Joint for Axillary Aneurism. 32. Whipple on Amputation at the Hip Joint. 3-3. Prof. Ehr-
mann on Successful Extirpation of a Polypous Tumour of the Larynx. 34. Bellingham on Compression in
Aneurism. 35. Orr^s Case of Tracheotomy. 36. Holmes Coote on Cancer of the Breast in the Male. .37.
Moore on Gunshot wound of the Lung, where the ball lodged fifty years. 33. On the Employment of Iodide
of Potassium in the Treatment of Syphilis. 39. Application of ice in the treatment of injuries. 40. Lenoiroa
Ununited Fracture successfully treated by Acupuncturation. 41. Prof. Syme on Amputation of the Thigh.
42. Curling'^s Case of Fatal Internal Strangulation caused by a cord prolonged from a Diverticulum of the
Ileum. 43. Golding Bird and John Hilton on Case of Internal Strangulation of Intestine relieved by Opera-
tion. 44. Fergussonon Strangulated Congenital Hernia in an infant seventeen days old, requirinp^ opera-
tion. 45. Guersant, Jr., on Surgical Treatment of Croup. 46. Geoghegan on Partial Amputation of the Foot.
47. Report of a Committee of the Surgical Society of Ireland, relative to the use and effects of Sulphuric
Ether.

Ophthalmology.— 48. Prof. Jacob on Foreign Bodies in the Eye. 49. Dixon''s Remarkable Case of Injury
of the Eye. 50. Szokalskion Obscurations of the Cornea in their Histological relations with reference to the
Practice of Ophthalmic Surgery. 51. Berncastle on Amauro sis from Hydatid Cyst in the Brain.

Midwifery.— 52. Robiquet on Remarkable case of spontaneous rupture of the Uterus during labour— Re-
covery. 53. Le Chaptois^ Case of Vaginal Entero-hysterocele reduced by taxis, and maintamed in place
by the introduction of sponges in the v agina. 54. K-iihne on Rupture of the Uterus— abdominal section —
recovery. 55. Czajewski on AVound of the Gravid Uterus — premature delivery — peritonitis— recovery. 56.
Bennett on Inflammatory Ulceration of the Cervix Uteri during Pregnancy, and on its Influence as a Cause
of Abortion. 67. Caesarian Operation performed by Mr. Skey, at St. Bartholomew's Hospital, the patient
being rendered insensible by ether. 58. Pochhammer on Congenital protrusion of the Liver through the
umbilical ring. 59. Caesarian Section. 60. iSowz on Lacerated Perineum. 61. DepowZ on Asphyxia neona-
torum. 62. Klencke on Diet in Infancy.

Medical Jurisprudence and Toxicology.— 63. Taylor on Contested identity determined by the teeth.
64. Blake on Poisons. 65. Delirium Tremens in an Infant. 66. Hamilton on the Echites Suberecta. 67.
Dupasquier on Vapours of Phosphorus, Lucifer Matches. 68. Thompson on the mode of testing the presence
of minute quantities of Alcohol. 69. Invalidity of a Contract made by a Lunatic. 70. Procuring of Abortion.
71. Lepage's Case of Poisoning by Arsenic relieved by the use of Magnesia. 72. Sale of Poisonous Sub-
stances.

Medical Education.— 73. The Edinburgh Statutes regarding the Degree. 74. Medical Organization in
Spain.

Foreign Correspondence.— Letters to the Editor from London. Sulphuric Ether in Surgical Operations
at Vienna.

American Intelligence— Original Communications.— ParJbnan's Anatomical Anomaly. Tyler''s Ante-
version of the Womb with adhesion of Os Uteri to body of 4th Lumbar Vertebra, &c.

Domestic Summary —Beck on Effects of Mercury on the Young Subject. Brainard on Amputation for
Scrofulous Diseases of the Joints. Baker on Case of Vicarious Menstruation from an Ulcer on the right
Mamma. Allen on Singular case of laceration of the Broad Ligaments. McLean on Blindness caused by
the use of Sulphate of Quinine. Harrison''s Speculations on the Cause of Yellow Fever. Herrick on Foreign
Bodies in the Organs and Tissues of the Body. Srvett on Case of Empyema in which the operation for Para-
centesis Thoracis failed from a cause not generally noticed. MPheeters on Rheumatism, with Hypertrophy
of both eyes. Draper on the Cause of the Circulation of the Blood. Little on Ischuria Renalis. Hogan on
Strychnine in Chorea. Deaderick on Excision of the Inferior Maxillary Bone for Osteo- Sarcoma. Cain on
Imperforate Prepuce. Couper on Medical Schools of the United States. Warren on Inhalation of Ether.
Burwell on Absence of one Kidney. Brainard on Dislocation of the Elbow. Gilman on Presentation of
the shoulder,— prolapsed Cord,— cord not pulsating, yet child born alive. National Medical Convention.
Delegates to National Medical Convention. Arrangements for the Meeting of the National Medical Con-
vention. Resignation of Professor Warren. New Medical Books.

LEA & BLANCHARD, Philadelphia.
THE TBRMS ARS

For the Medical Journal and the Medical News, if paid for in advance, (owing to the time of
issuing this advertisement, this year, amounts remitted before the first of July will be con-
sidered in advance,) .....-...- Five Dollars.
For the Journal only, when ordered without funds, or when paid for after the first of July, Five Dollars.
For the Medical News only, to be paid for free of postage, and always in advance, - One Dollar.
[JU* In no case can the News be sent without pay in advance. .£0

Or, persons sending Ten Dollars, before next July, can have both the Journal and the News for 1847 and
1848, together with nine numbers of the News for 1846, containing the first 228 pages of Todd and Bow-
man's Physiology.

Philadelphia, May, 1847

32 LEA & BLANCHARD'S PUBLICATIONS.

Two Medical Periodicals for Five Dollars a Year.

ONE GIVEN GRATIS.
THE

AMERICAN JOURNAL OF THE MEDICAL SCIENCES.

EDITED BY ISAAC HAYS, M. D.,

IS PUBLISHED QUARTERLY, ON THE FIRST OF JANUARY, APRIL,
JULY AND OCTOBER.

The number for January last contained over THREE HUNDRED large octavo pages, with twro plates ;
that for April consisted of two hundred and seventy -two pages. Illustrations on copper, stone, wood, &c.
are freely given, wherever required, and the whole is printed on fine white paper, with clear type.

ALSO,

THE MEDICAL NEWS AND LIBRARY|

A MONTHLY PERIODICAL OF THIRTY-TWO LARGE OCTAVO PAGES,
WITH NUMEROUS WOOD-CUTS,

Is given gratis to subscribers to the Journal, who pny in advance Five Dollars, free of expense to

the publishers.

It will thus be seen that subscribers obtain about FIFTEEN HUNDRED large sized and solid octavo
pages per annum, illustrated with fine engravings on wood, &c., for the low price of Five Dollars a year;
rendering these altogether among the CHEAPEST MEDICAL PERIODICALS PUBLISHED.

The Medical Journal is now in the twenty-ninth year of its existence, during the whole of which time it
has commanded the approbation of the profession at home and abroad. Appearing quarterly, its object is
to furnish its readers with a full and accurate resum6 of all interesting investigations and discoveries made
during the intervals, together with a choice selection of original papers. To this end, its pages are first
devoted to

ORIGINAL COMMUNICATIONS,

from correspondents in all parts of the Union, among whom it has numbered a large proportion of the pro-
minent members of the profession for many years past; it then furnishes REVIEWS and BIBLIOGRA-
PHICAL NO riCES of all new works of interest ; and lastly, it presents a very full and extended QUAR-
TERLY SUMMARY, consisting of a

RETROSPECT Al^D ABSTRACT

OF THE PROGRESS OF THE MEDICAL SGIENCESi

CAREFULLY COLLECTED FROM ALL THE
FOREIOIV AIVD DOMESTIC JOURlVAIiS.

This department is considered so practically useful, that no exertion is spared to render it as complete as
possible, so that both in extent and variety it may compare with any publications of a similar kind. The
shorter periods at which this journal appears, enables us to anticipate, by several months, from the original
sources, a large portion of the intelligence contained in the semi-annual publications of BRAITHWAITE
and RANKING, and the Annual Reports in the BRITISH AND FOREIGN MEDICAL REVIEW, DUB-
LIN MEDICAL JOURNAL, &c., and whatever of value is found in them, of which the original accounts
have not reached us, is at once taken and laid before our readers; besides much AMERICAN INTELLI-
GENCE, which is not likely to find its way across the Atlantic. The arrangements of the publishers for the
supply of this department, by purchase and exchange, are very extensive, embracing the principal Periodicals
of GREAT BRITAIN, FRANCE, GERMANY, DENMARK, ITALY, the EAST INDIES, &c.^ besides

ALL THE AMERICAN JOURNALS:

And especial attention will be given to make it as complete a digest as possible, of all the

IMPROVEMENTS AND DISCOVERIES IN MEDICAL SCIENCE.

Besides this, subscribers have the advantage of

THE naoNTSUM-s: zirsi^s,

Which furnishes the lighter and floating information, and embraces important books for

The Library Departmeiit.

The work now passing through its columns is

TODD AND BOWMAN'S
PHYSIOLOGICAL ANATOMY AND PHYSIOLOGY OF MAN,

WITH NUIHEROrS LARGE AND BEAUTIFUL WOOD-CUTS.

Each work in the Library is regularly paged, so as to be bound separately.

RETURN TO the circulation desk of any
University of California Library

or to the

NORTHERN REGIONAL LIBRARY FACILITY

BIdg. 400, Richmond Field Station

University of California

Richmond, CA 94804-4698

ALL BOOKS MAY BE RECALLED AFTER 7 DAYS
. 2-month loans may be renewed by calling

(510)642-6753
. 1-year loans may be recharged by bnnging

books to NRLF
. Renewals and recharges may be made

4 days prior to due date

DUE AS STAMPEDBELOW

APR 0 4 2003

JAN 1 7 2007

DD20 6M 9-03

QP34

C28

1846

Carpenter, W.B. 47600
Elements of physiology^

4 I v> * ' J

.,^y w:_ -■^'y:rJ^^-f^ v^..l»4:X^ ^\